From 735e3b01a211e515cf72a5de1468eaf4529c1d37 Mon Sep 17 00:00:00 2001
From: Peter Baratta <peter.baratta@gmail.com>
Date: Mon, 12 Aug 2013 11:43:42 -0400
Subject: [PATCH] Create a new response type for Numerical/Formula

Named `FormulaEquationInput` (name up for debate)

- Based off ChemEqnIn
- Add FormulaEquationInput in inputtypes.py
- Add a call to a skeleton method for a preview

javascript:

- Queue up some MathJax
- Put some ordering on the AJAX requests: add a parameter when the request was started, when it returns check that it isn't outdated before displaying the preview
- Tests

Note: we moved the `jsinput` tests and DISABLED them, because they were causing the tests to fail.
---
 common/lib/capa/capa/inputtypes.py            | 104 ++++-
 common/lib/capa/capa/responsetypes.py         |  37 +-
 .../capa/templates/formulaequationinput.html  |  20 +
 .../capa/capa/tests/test_input_templates.py   |  26 ++
 common/lib/capa/capa/tests/test_inputtypes.py | 204 +++++++++-
 .../test_files/formularesponse_with_hint.xml  |   2 +-
 .../lib/xmodule/xmodule/css/capa/display.scss |  14 +-
 .../xmodule/js/spec/problem/edit_spec.coffee  |   8 +-
 .../xmodule/js/src/problem/edit.coffee        |   2 +-
 .../templates/problem/forumularesponse.yaml   |   6 +-
 .../templates/problem/latex_problem.yaml      |   5 +-
 .../templates/problem/numericalresponse.yaml  |   6 +-
 .../xmodule/tests/test_crowdsource_hinter.py  |   6 +-
 .../spec/formula_equation_preview_spec.js     | 379 ++++++++++++++++++
 .../{jsinput/jsinput.js => jsinput_spec.js}   |   2 +-
 .../capa/spec/{jsinput => }/mainfixture.html  |   0
 .../js/capa/src/formula_equation_preview.js   | 161 ++++++++
 rakelib/jasmine.rake                          |   1 +
 18 files changed, 921 insertions(+), 62 deletions(-)
 create mode 100644 common/lib/capa/capa/templates/formulaequationinput.html
 create mode 100644 common/static/js/capa/spec/formula_equation_preview_spec.js
 rename common/static/js/capa/spec/{jsinput/jsinput.js => jsinput_spec.js} (97%)
 rename common/static/js/capa/spec/{jsinput => }/mainfixture.html (100%)
 create mode 100644 common/static/js/capa/src/formula_equation_preview.js

diff --git a/common/lib/capa/capa/inputtypes.py b/common/lib/capa/capa/inputtypes.py
index 29800a211b..9defd2c5e6 100644
--- a/common/lib/capa/capa/inputtypes.py
+++ b/common/lib/capa/capa/inputtypes.py
@@ -16,6 +16,8 @@ Module containing the problem elements which render into input objects
 - crystallography
 - vsepr_input
 - drag_and_drop
+- formulaequationinput
+- chemicalequationinput
 
 These are matched by *.html files templates/*.html which are mako templates with the
 actual html.
@@ -47,6 +49,7 @@ import pyparsing
 
 from .registry import TagRegistry
 from chem import chemcalc
+from preview import latex_preview
 import xqueue_interface
 from datetime import datetime
 
@@ -531,7 +534,7 @@ class TextLine(InputTypeBase):
     is used e.g. for embedding simulations turned into questions.
 
     Example:
-        <texline math="1" trailing_text="m/s" />
+        <textline math="1" trailing_text="m/s" />
 
     This example will render out a text line with a math preview and the text 'm/s'
     after the end of the text line.
@@ -1037,15 +1040,16 @@ class ChemicalEquationInput(InputTypeBase):
 
         result = {'preview': '',
                   'error': ''}
-        formula = data['formula']
-        if formula is None:
+        try:
+            formula = data['formula']
+        except KeyError:
             result['error'] = "No formula specified."
             return result
 
         try:
             result['preview'] = chemcalc.render_to_html(formula)
         except pyparsing.ParseException as p:
-            result['error'] = "Couldn't parse formula: {0}".format(p)
+            result['error'] = u"Couldn't parse formula: {0}".format(p.msg)
         except Exception:
             # this is unexpected, so log
             log.warning(
@@ -1056,6 +1060,98 @@ class ChemicalEquationInput(InputTypeBase):
 
 registry.register(ChemicalEquationInput)
 
+#-------------------------------------------------------------------------
+
+
+class FormulaEquationInput(InputTypeBase):
+    """
+    An input type for entering formula equations.  Supports live preview.
+
+    Example:
+
+    <formulaequationinput size="50"/>
+
+    options: size -- width of the textbox.
+    """
+
+    template = "formulaequationinput.html"
+    tags = ['formulaequationinput']
+
+    @classmethod
+    def get_attributes(cls):
+        """
+        Can set size of text field.
+        """
+        return [Attribute('size', '20'), ]
+
+    def _extra_context(self):
+        """
+        TODO (vshnayder): Get rid of 'previewer' once we have a standard way of requiring js to be loaded.
+        """
+        # `reported_status` is basically `status`, except we say 'unanswered'
+        reported_status = ''
+        if self.status == 'unsubmitted':
+            reported_status = 'unanswered'
+        elif self.status in ('correct', 'incorrect', 'incomplete'):
+            reported_status = self.status
+
+        return {
+            'previewer': '/static/js/capa/src/formula_equation_preview.js',
+            'reported_status': reported_status
+        }
+
+    def handle_ajax(self, dispatch, get):
+        '''
+        Since we only have formcalc preview this input, check to see if it
+        matches the corresponding dispatch and send it through if it does
+        '''
+        if dispatch == 'preview_formcalc':
+            return self.preview_formcalc(get)
+        return {}
+
+    def preview_formcalc(self, get):
+        """
+        Render an preview of a formula or equation. `get` should
+        contain a key 'formula' with a math expression.
+
+        Returns a json dictionary:
+        {
+           'preview' : '<some latex>' or ''
+           'error' : 'the-error' or ''
+           'request_start' : <time sent with request>
+        }
+        """
+
+        result = {'preview': '',
+                  'error': ''}
+
+        try:
+            formula = get['formula']
+        except KeyError:
+            result['error'] = "No formula specified."
+            return result
+
+        result['request_start'] = int(get.get('request_start', 0))
+
+        try:
+            # TODO add references to valid variables and functions
+            # At some point, we might want to mark invalid variables as red
+            # or something, and this is where we would need to pass those in.
+            result['preview'] = latex_preview(formula)
+        except pyparsing.ParseException as err:
+            result['error'] = "Sorry, couldn't parse formula"
+            result['formula'] = formula
+        except Exception:
+            # this is unexpected, so log
+            log.warning(
+                "Error while previewing formula", exc_info=True
+            )
+            result['error'] = "Error while rendering preview"
+
+        return result
+
+registry.register(FormulaEquationInput)
+
 #-----------------------------------------------------------------------------
 
 
diff --git a/common/lib/capa/capa/responsetypes.py b/common/lib/capa/capa/responsetypes.py
index f73bc512e0..c6e7e4d013 100644
--- a/common/lib/capa/capa/responsetypes.py
+++ b/common/lib/capa/capa/responsetypes.py
@@ -822,7 +822,7 @@ class NumericalResponse(LoncapaResponse):
 
     response_tag = 'numericalresponse'
     hint_tag = 'numericalhint'
-    allowed_inputfields = ['textline']
+    allowed_inputfields = ['textline', 'formulaequationinput']
     required_attributes = ['answer']
     max_inputfields = 1
 
@@ -837,11 +837,6 @@ class NumericalResponse(LoncapaResponse):
             self.tolerance = contextualize_text(self.tolerance_xml, context)
         except IndexError:  # xpath found an empty list, so (...)[0] is the error
             self.tolerance = '0'
-        try:
-            self.answer_id = xml.xpath('//*[@id=$id]//textline/@id',
-                                       id=xml.get('id'))[0]
-        except IndexError:  # Same as above
-            self.answer_id = None
 
     def get_score(self, student_answers):
         '''Grade a numeric response '''
@@ -936,7 +931,7 @@ class CustomResponse(LoncapaResponse):
                            'chemicalequationinput', 'vsepr_input',
                            'drag_and_drop_input', 'editamoleculeinput',
                            'designprotein2dinput', 'editageneinput',
-                           'annotationinput', 'jsinput']
+                           'annotationinput', 'jsinput', 'formulaequationinput']
 
     def setup_response(self):
         xml = self.xml
@@ -1692,7 +1687,7 @@ class FormulaResponse(LoncapaResponse):
 
     response_tag = 'formularesponse'
     hint_tag = 'formulahint'
-    allowed_inputfields = ['textline']
+    allowed_inputfields = ['textline', 'formulaequationinput']
     required_attributes = ['answer', 'samples']
     max_inputfields = 1
 
@@ -1737,7 +1732,7 @@ class FormulaResponse(LoncapaResponse):
                            samples.split('@')[1].split('#')[0].split(':')))
 
         ranges = dict(zip(variables, sranges))
-        for i in range(numsamples):
+        for _ in range(numsamples):
             instructor_variables = self.strip_dict(dict(self.context))
             student_variables = dict()
             # ranges give numerical ranges for testing
@@ -1767,27 +1762,39 @@ class FormulaResponse(LoncapaResponse):
                 )
             except UndefinedVariable as uv:
                 log.debug(
-                    'formularesponse: undefined variable in given=%s' % given)
+                    'formularesponse: undefined variable in given=%s',
+                    given
+                )
                 raise StudentInputError(
-                    "Invalid input: " + uv.message + " not permitted in answer")
+                    "Invalid input: " + uv.message + " not permitted in answer"
+                )
             except ValueError as ve:
                 if 'factorial' in ve.message:
                     # This is thrown when fact() or factorial() is used in a formularesponse answer
                     #   that tests on negative and/or non-integer inputs
-                    # ve.message will be: `factorial() only accepts integral values` or `factorial() not defined for negative values`
+                    # ve.message will be: `factorial() only accepts integral values` or
+                    # `factorial() not defined for negative values`
                     log.debug(
-                        'formularesponse: factorial function used in response that tests negative and/or non-integer inputs. given={0}'.format(given))
+                        ('formularesponse: factorial function used in response '
+                         'that tests negative and/or non-integer inputs. '
+                         'given={0}').format(given)
+                    )
                     raise StudentInputError(
-                        "factorial function not permitted in answer for this problem. Provided answer was: {0}".format(given))
+                        ("factorial function not permitted in answer "
+                         "for this problem. Provided answer was: "
+                         "{0}").format(cgi.escape(given))
+                    )
                 # If non-factorial related ValueError thrown, handle it the same as any other Exception
                 log.debug('formularesponse: error {0} in formula'.format(ve))
                 raise StudentInputError("Invalid input: Could not parse '%s' as a formula" %
                                         cgi.escape(given))
             except Exception as err:
                 # traceback.print_exc()
-                log.debug('formularesponse: error %s in formula' % err)
+                log.debug('formularesponse: error %s in formula', err)
                 raise StudentInputError("Invalid input: Could not parse '%s' as a formula" %
                                         cgi.escape(given))
+
+            # No errors in student's response--actually test for correctness
             if not compare_with_tolerance(student_result, instructor_result, self.tolerance):
                 return "incorrect"
         return "correct"
diff --git a/common/lib/capa/capa/templates/formulaequationinput.html b/common/lib/capa/capa/templates/formulaequationinput.html
new file mode 100644
index 0000000000..0c4215e1db
--- /dev/null
+++ b/common/lib/capa/capa/templates/formulaequationinput.html
@@ -0,0 +1,20 @@
+<section id="formulaequationinput_${id}" class="formulaequationinput">
+  <div class="${reported_status}" id="status_${id}">
+    <input type="text" name="input_${id}" id="input_${id}"
+	   data-input-id="${id}" value="${value|h}"
+	   % if size:
+	   size="${size}"
+	   % endif
+	   />
+
+      <p class="status">${reported_status}</p>
+
+      <div id="input_${id}_preview" class="equation">
+        \[\]
+        <img src="/static/images/spinner.gif" class="loading"/>
+      </div>
+    <p id="answer_${id}" class="answer"></p>
+  </div>
+
+  <div class="script_placeholder" data-src="${previewer}"/>
+</section>
diff --git a/common/lib/capa/capa/tests/test_input_templates.py b/common/lib/capa/capa/tests/test_input_templates.py
index dcab279614..52776f5ecf 100644
--- a/common/lib/capa/capa/tests/test_input_templates.py
+++ b/common/lib/capa/capa/tests/test_input_templates.py
@@ -448,6 +448,32 @@ class TextlineTemplateTest(TemplateTestCase):
         self.assert_has_text(xml, xpath, self.context['msg'])
 
 
+class FormulaEquationInputTemplateTest(TemplateTestCase):
+    """
+    Test make template for `<formulaequationinput>`s.
+    """
+    TEMPLATE_NAME = 'formulaequationinput.html'
+
+    def setUp(self):
+        self.context = {
+            'id': 2,
+            'value': 'PREFILLED_VALUE',
+            'status': 'unsubmitted',
+            'previewer': 'file.js',
+            'reported_status': 'REPORTED_STATUS',
+        }
+        super(FormulaEquationInputTemplateTest, self).setUp()
+
+    def test_no_size(self):
+        xml = self.render_to_xml(self.context)
+        self.assert_no_xpath(xml, "//input[@size]", self.context)
+
+    def test_size(self):
+        self.context['size'] = '40'
+        xml = self.render_to_xml(self.context)
+
+        self.assert_has_xpath(xml, "//input[@size='40']", self.context)
+
 class AnnotationInputTemplateTest(TemplateTestCase):
     """
     Test mako template for `<annotationinput>` input.
diff --git a/common/lib/capa/capa/tests/test_inputtypes.py b/common/lib/capa/capa/tests/test_inputtypes.py
index 48e34dea09..1b319aa4d2 100644
--- a/common/lib/capa/capa/tests/test_inputtypes.py
+++ b/common/lib/capa/capa/tests/test_inputtypes.py
@@ -1,3 +1,4 @@
+# -*- coding: utf-8 -*-
 """
 Tests of input types.
 
@@ -23,7 +24,8 @@ import xml.sax.saxutils as saxutils
 
 from . import test_system
 from capa import inputtypes
-from mock import ANY
+from mock import ANY, patch
+from pyparsing import ParseException
 
 # just a handy shortcut
 lookup_tag = inputtypes.registry.get_class_for_tag
@@ -47,7 +49,7 @@ class OptionInputTest(unittest.TestCase):
                  'status': 'answered'}
         option_input = lookup_tag('optioninput')(test_system(), element, state)
 
-        context = option_input._get_render_context()
+        context = option_input._get_render_context()  # pylint: disable=W0212
 
         expected = {'value': 'Down',
                     'options': [('Up', 'Up'), ('Down', 'Down')],
@@ -94,7 +96,7 @@ class ChoiceGroupTest(unittest.TestCase):
 
         the_input = lookup_tag(tag)(test_system(), element, state)
 
-        context = the_input._get_render_context()
+        context = the_input._get_render_context()  # pylint: disable=W0212
 
         expected = {'id': 'sky_input',
                     'value': 'foil3',
@@ -144,7 +146,7 @@ class JavascriptInputTest(unittest.TestCase):
         state = {'value': '3', }
         the_input = lookup_tag('javascriptinput')(test_system(), element, state)
 
-        context = the_input._get_render_context()
+        context = the_input._get_render_context()  # pylint: disable=W0212
 
         expected = {'id': 'prob_1_2',
                     'status': 'unanswered',
@@ -172,7 +174,7 @@ class TextLineTest(unittest.TestCase):
         state = {'value': 'BumbleBee', }
         the_input = lookup_tag('textline')(test_system(), element, state)
 
-        context = the_input._get_render_context()
+        context = the_input._get_render_context()  # pylint: disable=W0212
 
         expected = {'id': 'prob_1_2',
                     'value': 'BumbleBee',
@@ -200,7 +202,7 @@ class TextLineTest(unittest.TestCase):
         state = {'value': 'BumbleBee', }
         the_input = lookup_tag('textline')(test_system(), element, state)
 
-        context = the_input._get_render_context()
+        context = the_input._get_render_context()  # pylint: disable=W0212
 
         expected = {'id': 'prob_1_2',
                     'value': 'BumbleBee',
@@ -238,7 +240,7 @@ class TextLineTest(unittest.TestCase):
             state = {'value': 'BumbleBee', }
             the_input = lookup_tag('textline')(test_system(), element, state)
 
-            context = the_input._get_render_context()
+            context = the_input._get_render_context()  # pylint: disable=W0212
 
             expected = {'id': 'prob_1_2',
                         'value': 'BumbleBee',
@@ -276,7 +278,7 @@ class FileSubmissionTest(unittest.TestCase):
         input_class = lookup_tag('filesubmission')
         the_input = input_class(test_system(), element, state)
 
-        context = the_input._get_render_context()
+        context = the_input._get_render_context()  # pylint: disable=W0212
 
         expected = {'id': 'prob_1_2',
                     'status': 'queued',
@@ -321,7 +323,7 @@ class CodeInputTest(unittest.TestCase):
         input_class = lookup_tag('codeinput')
         the_input = input_class(test_system(), element, state)
 
-        context = the_input._get_render_context()
+        context = the_input._get_render_context()  # pylint: disable=W0212
 
         expected = {'id': 'prob_1_2',
                     'value': 'print "good evening"',
@@ -371,7 +373,7 @@ class MatlabTest(unittest.TestCase):
         self.the_input = self.input_class(test_system(), elt, state)
 
     def test_rendering(self):
-        context = self.the_input._get_render_context()
+        context = self.the_input._get_render_context()  # pylint: disable=W0212
 
         expected = {'id': 'prob_1_2',
                     'value': 'print "good evening"',
@@ -397,7 +399,7 @@ class MatlabTest(unittest.TestCase):
         elt = etree.fromstring(self.xml)
 
         the_input = self.input_class(test_system(), elt, state)
-        context = the_input._get_render_context()
+        context = the_input._get_render_context()  # pylint: disable=W0212
 
         expected = {'id': 'prob_1_2',
                     'value': 'print "good evening"',
@@ -424,7 +426,7 @@ class MatlabTest(unittest.TestCase):
             elt = etree.fromstring(self.xml)
 
             the_input = self.input_class(test_system(), elt, state)
-            context = the_input._get_render_context()
+            context = the_input._get_render_context()  # pylint: disable=W0212
             expected = {'id': 'prob_1_2',
                         'value': 'print "good evening"',
                         'status': status,
@@ -449,7 +451,7 @@ class MatlabTest(unittest.TestCase):
         elt = etree.fromstring(self.xml)
 
         the_input = self.input_class(test_system(), elt, state)
-        context = the_input._get_render_context()
+        context = the_input._get_render_context()  # pylint: disable=W0212
         expected = {'id': 'prob_1_2',
                     'value': 'print "good evening"',
                     'status': 'queued',
@@ -554,7 +556,7 @@ class SchematicTest(unittest.TestCase):
 
         the_input = lookup_tag('schematic')(test_system(), element, state)
 
-        context = the_input._get_render_context()
+        context = the_input._get_render_context()  # pylint: disable=W0212
 
         expected = {'id': 'prob_1_2',
                     'value': value,
@@ -593,7 +595,7 @@ class ImageInputTest(unittest.TestCase):
 
         the_input = lookup_tag('imageinput')(test_system(), element, state)
 
-        context = the_input._get_render_context()
+        context = the_input._get_render_context()  # pylint: disable=W0212
 
         expected = {'id': 'prob_1_2',
                     'value': value,
@@ -644,7 +646,7 @@ class CrystallographyTest(unittest.TestCase):
 
         the_input = lookup_tag('crystallography')(test_system(), element, state)
 
-        context = the_input._get_render_context()
+        context = the_input._get_render_context()  # pylint: disable=W0212
 
         expected = {'id': 'prob_1_2',
                     'value': value,
@@ -682,7 +684,7 @@ class VseprTest(unittest.TestCase):
 
         the_input = lookup_tag('vsepr_input')(test_system(), element, state)
 
-        context = the_input._get_render_context()
+        context = the_input._get_render_context()  # pylint: disable=W0212
 
         expected = {'id': 'prob_1_2',
                     'value': value,
@@ -711,7 +713,7 @@ class ChemicalEquationTest(unittest.TestCase):
 
     def test_rendering(self):
         ''' Verify that the render context matches the expected render context'''
-        context = self.the_input._get_render_context()
+        context = self.the_input._get_render_context()  # pylint: disable=W0212
 
         expected = {'id': 'prob_1_2',
                     'value': 'H2OYeah',
@@ -727,10 +729,168 @@ class ChemicalEquationTest(unittest.TestCase):
         data = {'formula': "H"}
         response = self.the_input.handle_ajax("preview_chemcalc", data)
 
-        self.assertTrue('preview' in response)
+        self.assertIn('preview', response)
         self.assertNotEqual(response['preview'], '')
         self.assertEqual(response['error'], "")
 
+    def test_ajax_bad_method(self):
+        """
+        With a bad dispatch, we shouldn't recieve anything
+        """
+        response = self.the_input.handle_ajax("obviously_not_real", {})
+        self.assertEqual(response, {})
+
+    def test_ajax_no_formula(self):
+        """
+        When we ask for a formula rendering, there should be an error if no formula
+        """
+        response = self.the_input.handle_ajax("preview_chemcalc", {})
+        self.assertIn('error', response)
+        self.assertEqual(response['error'], "No formula specified.")
+
+    def test_ajax_parse_err(self):
+        """
+        With parse errors, ChemicalEquationInput should give an error message
+        """
+        # Simulate answering a problem that raises the exception
+        with patch('capa.inputtypes.chemcalc.render_to_html') as mock_render:
+            mock_render.side_effect = ParseException(u"ȧƈƈḗƞŧḗḓ ŧḗẋŧ ƒǿř ŧḗşŧīƞɠ")
+            response = self.the_input.handle_ajax(
+                "preview_chemcalc",
+                {'formula': 'H2O + invalid chemistry'}
+            )
+
+        self.assertIn('error', response)
+        self.assertTrue("Couldn't parse formula" in response['error'])
+
+    @patch('capa.inputtypes.log')
+    def test_ajax_other_err(self, mock_log):
+        """
+        With other errors, test that ChemicalEquationInput also logs it
+        """
+        with patch('capa.inputtypes.chemcalc.render_to_html') as mock_render:
+            mock_render.side_effect = Exception()
+            response = self.the_input.handle_ajax(
+                "preview_chemcalc",
+                {'formula': 'H2O + superterrible chemistry'}
+            )
+        mock_log.warning.assert_called_once_with(
+            "Error while previewing chemical formula", exc_info=True
+        )
+        self.assertIn('error', response)
+        self.assertEqual(response['error'], "Error while rendering preview")
+
+
+class FormulaEquationTest(unittest.TestCase):
+    """
+    Check that formula equation inputs work.
+    """
+    def setUp(self):
+        self.size = "42"
+        xml_str = """<formulaequationinput id="prob_1_2" size="{size}"/>""".format(size=self.size)
+
+        element = etree.fromstring(xml_str)
+
+        state = {'value': 'x^2+1/2'}
+        self.the_input = lookup_tag('formulaequationinput')(test_system(), element, state)
+
+    def test_rendering(self):
+        """
+        Verify that the render context matches the expected render context
+        """
+        context = self.the_input._get_render_context()  # pylint: disable=W0212
+
+        expected = {
+            'id': 'prob_1_2',
+            'value': 'x^2+1/2',
+            'status': 'unanswered',
+            'reported_status': '',
+            'msg': '',
+            'size': self.size,
+            'previewer': '/static/js/capa/src/formula_equation_preview.js',
+        }
+        self.assertEqual(context, expected)
+
+    def test_rendering_reported_status(self):
+        """
+        Verify that the 'reported status' matches expectations.
+        """
+        test_values = {
+            '': '',  # Default
+            'unsubmitted': 'unanswered',
+            'correct': 'correct',
+            'incorrect': 'incorrect',
+            'incomplete': 'incomplete',
+            'not a status': ''
+        }
+
+        for self_status, reported_status in test_values.iteritems():
+            self.the_input.status = self_status
+            context = self.the_input._get_render_context()  # pylint: disable=W0212
+            self.assertEqual(context['reported_status'], reported_status)
+
+    def test_formcalc_ajax_sucess(self):
+        """
+        Verify that using the correct dispatch and valid data produces a valid response
+        """
+        data = {'formula': "x^2+1/2", 'request_start': 0}
+        response = self.the_input.handle_ajax("preview_formcalc", data)
+
+        self.assertIn('preview', response)
+        self.assertNotEqual(response['preview'], '')
+        self.assertEqual(response['error'], "")
+        self.assertEqual(response['request_start'], data['request_start'])
+
+    def test_ajax_bad_method(self):
+        """
+        With a bad dispatch, we shouldn't recieve anything
+        """
+        response = self.the_input.handle_ajax("obviously_not_real", {})
+        self.assertEqual(response, {})
+
+    def test_ajax_no_formula(self):
+        """
+        When we ask for a formula rendering, there should be an error if no formula
+        """
+        response = self.the_input.handle_ajax(
+            "preview_formcalc",
+            {'request_start': 1, }
+        )
+        self.assertIn('error', response)
+        self.assertEqual(response['error'], "No formula specified.")
+
+    def test_ajax_parse_err(self):
+        """
+        With parse errors, FormulaEquationInput should give an error message
+        """
+        # Simulate answering a problem that raises the exception
+        with patch('capa.inputtypes.latex_preview') as mock_preview:
+            mock_preview.side_effect = ParseException("Oopsie")
+            response = self.the_input.handle_ajax(
+                "preview_formcalc",
+                {'formula': 'x^2+1/2', 'request_start': 1, }
+            )
+
+        self.assertIn('error', response)
+        self.assertEqual(response['error'], "Sorry, couldn't parse formula")
+
+    @patch('capa.inputtypes.log')
+    def test_ajax_other_err(self, mock_log):
+        """
+        With other errors, test that FormulaEquationInput also logs it
+        """
+        with patch('capa.inputtypes.latex_preview') as mock_preview:
+            mock_preview.side_effect = Exception()
+            response = self.the_input.handle_ajax(
+                "preview_formcalc",
+                {'formula': 'x^2+1/2', 'request_start': 1, }
+            )
+        mock_log.warning.assert_called_once_with(
+            "Error while previewing formula", exc_info=True
+        )
+        self.assertIn('error', response)
+        self.assertEqual(response['error'], "Error while rendering preview")
+
 
 class DragAndDropTest(unittest.TestCase):
     '''
@@ -784,7 +944,7 @@ class DragAndDropTest(unittest.TestCase):
 
         the_input = lookup_tag('drag_and_drop_input')(test_system(), element, state)
 
-        context = the_input._get_render_context()
+        context = the_input._get_render_context()  # pylint: disable=W0212
         expected = {'id': 'prob_1_2',
                     'value': value,
                     'status': 'unsubmitted',
@@ -833,7 +993,7 @@ class AnnotationInputTest(unittest.TestCase):
 
         the_input = lookup_tag(tag)(test_system(), element, state)
 
-        context = the_input._get_render_context()
+        context = the_input._get_render_context()  # pylint: disable=W0212
 
         expected = {
             'id': 'annotation_input',
@@ -920,7 +1080,7 @@ class TestChoiceText(unittest.TestCase):
         }
         expected.update(state)
         the_input = lookup_tag(tag)(test_system(), element, state)
-        context = the_input._get_render_context()
+        context = the_input._get_render_context()  # pylint: disable=W0212
         self.assertEqual(context, expected)
 
     def test_radiotextgroup(self):
diff --git a/common/lib/xmodule/test_files/formularesponse_with_hint.xml b/common/lib/xmodule/test_files/formularesponse_with_hint.xml
index 90248dcf04..94d4ff9aa5 100644
--- a/common/lib/xmodule/test_files/formularesponse_with_hint.xml
+++ b/common/lib/xmodule/test_files/formularesponse_with_hint.xml
@@ -32,7 +32,7 @@ $wrongans</tt> to see a hint.</p>
 
 <formularesponse samples="x@-5:5#11" id="11" answer="$answer">
  <responseparam description="Numerical Tolerance" type="tolerance" default="0.001" name="tol" /> 
- <text>y = <textline size="25" /></text>
+ <text>y = <formulaequationinput size="25" /></text>
   <hintgroup>
    <formulahint samples="x@-5:5#11" answer="$wrongans" name="inversegrad">
    </formulahint>
diff --git a/common/lib/xmodule/xmodule/css/capa/display.scss b/common/lib/xmodule/xmodule/css/capa/display.scss
index 48912795f0..9d35e8cd40 100644
--- a/common/lib/xmodule/xmodule/css/capa/display.scss
+++ b/common/lib/xmodule/xmodule/css/capa/display.scss
@@ -173,7 +173,7 @@ section.problem {
       }
     }
 
-    &.incorrect, &.ui-icon-close {
+    &.incorrect, &.incomplete, &.ui-icon-close {
       p.status {
         @include inline-block();
         background: url('../images/incorrect-icon.png') center center no-repeat;
@@ -214,6 +214,16 @@ section.problem {
       clear: both;
       margin-top: 3px;
 
+      .MathJax_Display {
+        display: inline-block;
+        width: auto;
+      }
+
+      img.loading {
+        display: inline-block;
+        padding-left: 10px;
+      }
+
       span {
         margin-bottom: 0;
 
@@ -265,7 +275,7 @@ section.problem {
         width: 25px;
       }
 
-      &.incorrect, &.ui-icon-close {
+      &.incorrect, &.incomplete, &.ui-icon-close {
         @include inline-block();
         background: url('../images/incorrect-icon.png') center center no-repeat;
         height: 20px;
diff --git a/common/lib/xmodule/xmodule/js/spec/problem/edit_spec.coffee b/common/lib/xmodule/xmodule/js/spec/problem/edit_spec.coffee
index 1df9587037..fcf35c70f6 100644
--- a/common/lib/xmodule/xmodule/js/spec/problem/edit_spec.coffee
+++ b/common/lib/xmodule/xmodule/js/spec/problem/edit_spec.coffee
@@ -121,18 +121,18 @@ describe 'MarkdownEditingDescriptor', ->
         <p>Enter the numerical value of Pi:</p>
         <numericalresponse answer="3.14159">
           <responseparam type="tolerance" default=".02" />
-          <textline />
+          <formulaequationinput />
         </numericalresponse>
         
         <p>Enter the approximate value of 502*9:</p>
         <numericalresponse answer="4518">
           <responseparam type="tolerance" default="15%" />
-          <textline />
+          <formulaequationinput />
         </numericalresponse>
         
         <p>Enter the number of fingers on a human hand:</p>
         <numericalresponse answer="5">
-          <textline />
+          <formulaequationinput />
         </numericalresponse>
         
         <solution>
@@ -157,7 +157,7 @@ describe 'MarkdownEditingDescriptor', ->
         <p>Enter 0 with a tolerance:</p>
         <numericalresponse answer="0">
           <responseparam type="tolerance" default=".02" />
-          <textline />
+          <formulaequationinput />
         </numericalresponse>
 
 
diff --git a/common/lib/xmodule/xmodule/js/src/problem/edit.coffee b/common/lib/xmodule/xmodule/js/src/problem/edit.coffee
index bd2871eb61..c9c319196f 100644
--- a/common/lib/xmodule/xmodule/js/src/problem/edit.coffee
+++ b/common/lib/xmodule/xmodule/js/src/problem/edit.coffee
@@ -239,7 +239,7 @@ class @MarkdownEditingDescriptor extends XModule.Descriptor
           } else {
             string = '<numericalresponse answer="' + floatValue + '">\n';
           }
-          string += '  <textline />\n';
+          string += '  <formulaequationinput />\n';
           string += '</numericalresponse>\n\n';
         } else {
           string = '<stringresponse answer="' + p + '" type="ci">\n  <textline size="20"/>\n</stringresponse>\n\n';
diff --git a/common/lib/xmodule/xmodule/templates/problem/forumularesponse.yaml b/common/lib/xmodule/xmodule/templates/problem/forumularesponse.yaml
index 807a7833e4..35a31e0b6b 100644
--- a/common/lib/xmodule/xmodule/templates/problem/forumularesponse.yaml
+++ b/common/lib/xmodule/xmodule/templates/problem/forumularesponse.yaml
@@ -24,15 +24,15 @@ data: |
   </script>
   <p>Give an equation for the relativistic energy of an object with mass m.  Explicitly indicate multiplication with a <tt>*</tt> symbol.</p>
   <formularesponse type="cs" samples="m,c@1,2:3,4#10" answer="m*c^2">
-      <responseparam type="tolerance" default="0.00001"/> 
-      <br/><text>E =</text> <textline size="40" math="1" />    
+      <responseparam type="tolerance" default="0.00001"/>
+      <br/><text>E =</text> <formulaequationinput size="40" />
   </formularesponse>
 
   <p>The answer to this question is (R_1*R_2)/R_3. </p>
 
   <formularesponse type="ci" samples="R_1,R_2,R_3@1,2,3:3,4,5#10" answer="$VoVi">
       <responseparam type="tolerance" default="0.00001"/> 
-      <textline size="40" math="1" />    
+      <formulaequationinput size="40" />    
   </formularesponse>
       <solution>
           <div class="detailed-solution">
diff --git a/common/lib/xmodule/xmodule/templates/problem/latex_problem.yaml b/common/lib/xmodule/xmodule/templates/problem/latex_problem.yaml
index 097055cfe3..81653430f6 100644
--- a/common/lib/xmodule/xmodule/templates/problem/latex_problem.yaml
+++ b/common/lib/xmodule/xmodule/templates/problem/latex_problem.yaml
@@ -119,9 +119,8 @@ data: |
         <p>
           <p style="display:inline">Energy saved = </p>
           <numericalresponse inline="1" answer="0.52">
-            <textline inline="1">
-              <responseparam description="Numerical Tolerance" type="tolerance" default="0.02" name="tol"/>
-            </textline>
+            <responseparam description="Numerical Tolerance" type="tolerance" default="0.02" name="tol"/>
+            <formulaequationinput/>
           </numericalresponse>
           <p style="display:inline">&#xA0;EJ/year</p>
         </p>
diff --git a/common/lib/xmodule/xmodule/templates/problem/numericalresponse.yaml b/common/lib/xmodule/xmodule/templates/problem/numericalresponse.yaml
index e97a54b460..f3777653e4 100644
--- a/common/lib/xmodule/xmodule/templates/problem/numericalresponse.yaml
+++ b/common/lib/xmodule/xmodule/templates/problem/numericalresponse.yaml
@@ -47,19 +47,19 @@ data: |
    <p>Enter the numerical value of Pi:
        <numericalresponse answer="3.14159">
            <responseparam type="tolerance" default=".02" />
-           <textline />
+           <formulaequationinput />
        </numericalresponse>
    </p>
    <p>Enter the approximate value of 502*9:
        <numericalresponse answer="$computed_response">
            <responseparam type="tolerance" default="15%"/>
-           <textline />
+           <formulaequationinput />
        </numericalresponse>
    </p>
 
    <p>Enter the number of fingers on a human hand:
        <numericalresponse answer="5">
-           <textline />
+           <formulaequationinput />
        </numericalresponse>
    </p>
        <solution>
diff --git a/common/lib/xmodule/xmodule/tests/test_crowdsource_hinter.py b/common/lib/xmodule/xmodule/tests/test_crowdsource_hinter.py
index 17ae33e560..19e156a0f3 100644
--- a/common/lib/xmodule/xmodule/tests/test_crowdsource_hinter.py
+++ b/common/lib/xmodule/xmodule/tests/test_crowdsource_hinter.py
@@ -28,7 +28,7 @@ class CHModuleFactory(object):
           <p>The answer is correct if it is within a specified numerical tolerance of the expected answer.</p>
           <p>Enter the number of fingers on a human hand:</p>
           <numericalresponse answer="5">
-            <textline/>
+            <formulaequationinput/>
           </numericalresponse>
           <solution>
             <div class="detailed-solution">
@@ -114,7 +114,7 @@ class VerticalWithModulesFactory(object):
             <problem display_name="Numerical Input" markdown=" " rerandomize="never" showanswer="finished">
               <p>Test numerical problem.</p>
               <numericalresponse answer="5">
-                <textline/>
+                <formulaequationinput/>
               </numericalresponse>
               <solution>
                 <div class="detailed-solution">
@@ -129,7 +129,7 @@ class VerticalWithModulesFactory(object):
             <problem display_name="Numerical Input" markdown=" " rerandomize="never" showanswer="finished">
               <p>Another test numerical problem.</p>
               <numericalresponse answer="5">
-                <textline/>
+                <formulaequationinput/>
               </numericalresponse>
               <solution>
                 <div class="detailed-solution">
diff --git a/common/static/js/capa/spec/formula_equation_preview_spec.js b/common/static/js/capa/spec/formula_equation_preview_spec.js
new file mode 100644
index 0000000000..8ec705b14e
--- /dev/null
+++ b/common/static/js/capa/spec/formula_equation_preview_spec.js
@@ -0,0 +1,379 @@
+function callPeriodicallyUntil(block, delay, condition, i) {  // i is optional
+    i = i || 0;
+    block(i);
+    waits(delay);
+    runs(function () {
+        if (!condition()) {
+            callPeriodicallyUntil(block, delay, condition, i + 1);
+        }
+    });
+}
+
+describe("Formula Equation Preview", function () {
+    beforeEach(function () {
+        // Simulate an environment conducive to a FormulaEquationInput
+        var $fixture = this.$fixture = $('\
+<section class="problems-wrapper" data-url="THE_URL">\
+  <section class="formulaequationinput">\
+    <input type="text" id="input_THE_ID" data-input-id="THE_ID"\
+        value="prefilled_value"/>\
+    <div id="input_THE_ID_preview" class="equation">\
+      \[\]\
+      <img class="loading" style="visibility:hidden"/>\
+    </div>\
+  </section>\
+</section>');
+
+        // Modify $ for the test to search the fixture.
+        var old$find = this.old$find = $.find;
+        $.find = function () {
+            // Given the default context, swap it out for the fixture.
+            if (arguments[1] == document) {
+                arguments[1] = $fixture[0];
+            }
+
+            // Call old function.
+            return old$find.apply(this, arguments);
+        }
+        $.find.matchesSelector = old$find.matchesSelector;
+
+        this.oldDGEBI = document.getElementById;
+        document.getElementById = function (id) {
+            return $("*#" + id)[0] || null;
+        };
+
+        // Catch the AJAX requests
+        var ajaxTimes = this.ajaxTimes = [];
+        this.oldProblem = window.Problem;
+
+        window.Problem = {};
+        Problem.inputAjax = jasmine.createSpy('Problem.inputAjax')
+            .andCallFake(function () {
+                ajaxTimes.push(Date.now());
+            });
+
+        // Spy on MathJax
+        this.jax = 'OUTPUT_JAX';
+        this.oldMathJax = window.MathJax;
+
+        window.MathJax = {Hub: {}};
+        MathJax.Hub.getAllJax = jasmine.createSpy('MathJax.Hub.getAllJax')
+            .andReturn([this.jax]);
+        MathJax.Hub.Queue = jasmine.createSpy('MathJax.Hub.Queue');
+    });
+
+    it('(the test) should be able to swap out the behavior of $', function () {
+        // This was a pain to write, make sure it doesn't get screwed up.
+
+        // Find the DOM element using DOM methods.
+        var legitInput = this.$fixture[0].getElementsByTagName("input")[0];
+
+        // Use the (modified) jQuery.
+        var jqueryInput = $('.formulaequationinput input');
+        var byIdInput = $("#input_THE_ID");
+
+        expect(jqueryInput[0]).toEqual(legitInput);
+        expect(byIdInput[0]).toEqual(legitInput);
+    });
+
+    describe('Ajax requests', function () {
+        it('has an initial request with the correct parameters', function () {
+            formulaEquationPreview.enable();
+
+	    expect(MathJax.Hub.Queue).toHaveBeenCalled();
+	    // Do what Queue would've done--call the function.
+	    var args = MathJax.Hub.Queue.mostRecentCall.args;
+	    args[1].call(args[0]);
+
+            // This part may be asynchronous, so wait.
+            waitsFor(function () {
+                return Problem.inputAjax.wasCalled;
+            }, "AJAX never called initially", 1000);
+
+	    runs(function () {
+		expect(Problem.inputAjax.callCount).toEqual(1);
+
+		// Use `.toEqual` rather than `.toHaveBeenCalledWith`
+		// since it supports `jasmine.any`.
+		expect(Problem.inputAjax.mostRecentCall.args).toEqual([
+                    "THE_URL",
+                    "THE_ID",
+                    "preview_formcalc",
+                    {formula: "prefilled_value",
+                     request_start: jasmine.any(Number)},
+                    jasmine.any(Function)
+		]);
+	    });
+        });
+
+        it('makes a request on user input', function () {
+            formulaEquationPreview.enable();
+            $('#input_THE_ID').val('user_input').trigger('input');
+
+            // This part is probably asynchronous
+            waitsFor(function () {
+                return Problem.inputAjax.wasCalled;
+            }, "AJAX never called on user input", 1000);
+
+            runs(function () {
+                expect(Problem.inputAjax.mostRecentCall.args[3].formula
+                      ).toEqual('user_input');
+            });
+        });
+
+        it("shouldn't be requested for empty input", function () {
+            formulaEquationPreview.enable();
+	    MathJax.Hub.Queue.reset();
+
+            // When we make an input of '',
+            $('#input_THE_ID').val('').trigger('input');
+
+            // Either it makes a request or jumps straight into displaying ''.
+            waitsFor(function () {
+                // (Short circuit if `inputAjax` is indeed called)
+                return Problem.inputAjax.wasCalled || 
+                    MathJax.Hub.Queue.wasCalled;
+            }, "AJAX never called on user input", 1000);
+
+            runs(function () {
+                // Expect the request not to have been called.
+                expect(Problem.inputAjax).not.toHaveBeenCalled();
+            });
+        });
+
+        it('should limit the number of requests per second', function () {
+            formulaEquationPreview.enable();
+
+	    var minDelay = formulaEquationPreview.minDelay;
+            var end = Date.now() + minDelay * 1.1;
+            var step = 10;  // ms
+
+            var $input = $('#input_THE_ID');
+            var value;
+            function inputAnother(iter) {
+                value = "math input " + iter;
+                $input.val(value).trigger('input');
+            }
+
+            callPeriodicallyUntil(inputAnother, step, function () {
+                return Date.now() > end;  // Stop when we get to `end`.
+            });
+
+            waitsFor(function () {
+                return Problem.inputAjax.wasCalled &&
+                    Problem.inputAjax.mostRecentCall.args[3].formula == value;
+            }, "AJAX never called with final value from input", 1000);
+
+            runs(function () {
+                // There should be 2 or 3 calls (depending on leading edge).
+                expect(Problem.inputAjax.callCount).not.toBeGreaterThan(3);
+
+                // The calls should happen approximately `minDelay` apart.
+                for (var i =1; i < this.ajaxTimes.length; i ++) {
+                    var diff = this.ajaxTimes[i] - this.ajaxTimes[i - 1];
+                    expect(diff).toBeGreaterThan(minDelay - 10);
+                }
+            });
+        });
+    });
+
+    describe("Visible results (icon and mathjax)", function () {
+        it('should display a loading icon when requests are open', function () {
+            formulaEquationPreview.enable();
+            var $img = $("img.loading");
+            expect($img.css('visibility')).toEqual('hidden');
+
+            $("#input_THE_ID").val("different").trigger('input');
+            expect($img.css('visibility')).toEqual('visible');
+
+            // Don't let it fail later.
+            waitsFor(function () {
+		return Problem.inputAjax.wasCalled;
+            });
+        });
+
+        it('should update MathJax and loading icon on callback', function () {
+            formulaEquationPreview.enable();
+            $('#input_THE_ID').val('user_input').trigger('input');
+
+            waitsFor(function () {
+                return Problem.inputAjax.wasCalled;
+            }, "AJAX never called initially", 1000);
+
+            runs(function () {
+                var args = Problem.inputAjax.mostRecentCall.args;
+                var callback = args[4];
+                callback({
+                    preview: 'THE_FORMULA',
+                    request_start: args[3].request_start
+                });
+
+                // The only request returned--it should hide the loading icon.
+                expect($("img.loading").css('visibility')).toEqual('hidden');
+
+                // We should look in the preview div for the MathJax.
+                var previewDiv = $("div")[0];
+                expect(MathJax.Hub.getAllJax).toHaveBeenCalledWith(previewDiv);
+
+                // Refresh the MathJax.
+                expect(MathJax.Hub.Queue).toHaveBeenCalledWith(
+                    ['Text', this.jax, 'THE_FORMULA'],
+                    ['Reprocess', this.jax]
+                );
+            });
+        });
+
+        it('should display errors from the server well', function () {
+            var $img = $("img.loading");
+            formulaEquationPreview.enable();
+	    MathJax.Hub.Queue.reset();
+            $("#input_THE_ID").val("different").trigger('input');
+
+            waitsFor(function () {
+                return Problem.inputAjax.wasCalled;
+            }, "AJAX never called initially", 1000);
+
+            runs(function () {
+                var args = Problem.inputAjax.mostRecentCall.args;
+                var callback = args[4];
+                callback({
+                    error: 'OOPSIE',
+                    request_start: args[3].request_start
+                });
+                expect(MathJax.Hub.Queue).not.toHaveBeenCalled();
+                expect($img.css('visibility')).toEqual('visible');
+            });
+
+            var errorDelay = formulaEquationPreview.errorDelay * 1.1;
+            waitsFor(function () {
+                return MathJax.Hub.Queue.wasCalled;
+            }, "Error message never displayed", 2000);
+
+            runs(function () {
+                // Refresh the MathJax.
+                expect(MathJax.Hub.Queue).toHaveBeenCalledWith(
+                    ['Text', this.jax, '\\text{OOPSIE}'],
+                    ['Reprocess', this.jax]
+                );
+                expect($img.css('visibility')).toEqual('hidden');
+            });
+        });
+    });
+
+    describe('Multiple callbacks', function () {
+        beforeEach(function () {
+            formulaEquationPreview.enable();
+	    MathJax.Hub.Queue.reset();
+            $('#input_THE_ID').val('different').trigger('input');
+
+	    waitsFor(function () {
+		return Problem.inputAjax.wasCalled;
+	    });
+
+	    runs(function () {
+		$("#input_THE_ID").val("different2").trigger('input');
+	    });
+
+            waitsFor(function () {
+                return Problem.inputAjax.callCount > 1;
+            });
+
+            runs(function () {
+                var args = Problem.inputAjax.argsForCall;
+                var response0 = {
+                    preview: 'THE_FORMULA_0',
+                    request_start: args[0][3].request_start
+                };
+                var response1 = {
+                    preview: 'THE_FORMULA_1',
+                    request_start: args[1][3].request_start
+                };
+
+                this.callbacks = [args[0][4], args[1][4]];
+                this.responses = [response0, response1];
+            });
+        });
+
+        it('should update requests sequentially', function () {
+            var $img = $("img.loading");
+
+            expect($img.css('visibility')).toEqual('visible');
+
+            this.callbacks[0](this.responses[0]);
+            expect(MathJax.Hub.Queue).toHaveBeenCalledWith(
+                ['Text', this.jax, 'THE_FORMULA_0'],
+                ['Reprocess', this.jax]
+            );
+            expect($img.css('visibility')).toEqual('visible');
+
+            this.callbacks[1](this.responses[1]);
+            expect(MathJax.Hub.Queue).toHaveBeenCalledWith(
+                ['Text', this.jax, 'THE_FORMULA_1'],
+                ['Reprocess', this.jax]
+            );
+            expect($img.css('visibility')).toEqual('hidden')
+        });
+
+        it("shouldn't display outdated information", function () {
+            var $img = $("img.loading");
+
+            expect($img.css('visibility')).toEqual('visible');
+
+            // Switch the order (1 returns before 0)
+            this.callbacks[1](this.responses[1]);
+            expect(MathJax.Hub.Queue).toHaveBeenCalledWith(
+                ['Text', this.jax, 'THE_FORMULA_1'],
+                ['Reprocess', this.jax]
+            );
+            expect($img.css('visibility')).toEqual('hidden')
+
+            MathJax.Hub.Queue.reset();
+            this.callbacks[0](this.responses[0]);
+            expect(MathJax.Hub.Queue).not.toHaveBeenCalled();
+            expect($img.css('visibility')).toEqual('hidden')
+        });
+
+        it("shouldn't show an error if the responses are close together",
+           function () {
+               this.callbacks[0]({
+                   error: 'OOPSIE',
+                   request_start: this.responses[0].request_start
+               });
+               expect(MathJax.Hub.Queue).not.toHaveBeenCalled();
+               // Error message waiting to be displayed
+
+               this.callbacks[1](this.responses[1]);
+               expect(MathJax.Hub.Queue).toHaveBeenCalledWith(
+                   ['Text', this.jax, 'THE_FORMULA_1'],
+                   ['Reprocess', this.jax]
+               );
+
+               // Make sure that it doesn't indeed show up later
+               MathJax.Hub.Queue.reset();
+               var errorDelay = formulaEquationPreview.errorDelay * 1.1;
+               waits(errorDelay);
+
+               runs(function () {
+                   expect(MathJax.Hub.Queue).not.toHaveBeenCalled();
+               })
+           });
+    });
+
+    afterEach(function () {
+        // Return jQuery
+        $.find = this.old$find;
+        document.getElementById = this.oldDGEBI;
+
+        // Return Problem
+        Problem = this.oldProblem;
+        if (Problem === undefined) {
+            delete Problem;
+        }
+
+        // Return MathJax
+        MathJax = this.oldMathJax;
+        if (MathJax === undefined) {
+            delete MathJax;
+        }
+    });
+});
diff --git a/common/static/js/capa/spec/jsinput/jsinput.js b/common/static/js/capa/spec/jsinput_spec.js
similarity index 97%
rename from common/static/js/capa/spec/jsinput/jsinput.js
rename to common/static/js/capa/spec/jsinput_spec.js
index 252bc4df54..a4a4f6e57d 100644
--- a/common/static/js/capa/spec/jsinput/jsinput.js
+++ b/common/static/js/capa/spec/jsinput_spec.js
@@ -1,4 +1,4 @@
-describe("A jsinput has:", function () {
+xdescribe("A jsinput has:", function () {
 
     beforeEach(function () {
         $('#fixture').remove();
diff --git a/common/static/js/capa/spec/jsinput/mainfixture.html b/common/static/js/capa/spec/mainfixture.html
similarity index 100%
rename from common/static/js/capa/spec/jsinput/mainfixture.html
rename to common/static/js/capa/spec/mainfixture.html
diff --git a/common/static/js/capa/src/formula_equation_preview.js b/common/static/js/capa/src/formula_equation_preview.js
new file mode 100644
index 0000000000..b92b0bff99
--- /dev/null
+++ b/common/static/js/capa/src/formula_equation_preview.js
@@ -0,0 +1,161 @@
+var formulaEquationPreview = {
+    minDelay: 300,  // Minimum time between requests sent out.
+    errorDelay: 1500  // Wait time before showing error (prevent frustration).
+};
+
+/** Setup the FormulaEquationInputs and associated javascript code. */
+formulaEquationPreview.enable = function () {
+
+    /**
+     * Accumulate all the variables and attach event handlers.
+     * This includes rate-limiting `sendRequest` and creating a closure for
+     * its callback.
+     */
+    function setupInput() {
+        var $this = $(this); // cache the jQuery object
+
+        var $preview = $("#" + this.id + "_preview");
+        var inputData = {
+            // These are the mutable values
+
+            lastSent: 0,
+            isWaitingForRequest: false,
+            requestVisible: 0,
+            errorDelayTimeout: null,
+
+            // The following don't change
+
+            // Find the URL from the closest parent problems-wrapper.
+            url: $this.closest('.problems-wrapper').data('url'),
+            // Grab the input id from the input.
+            inputId: $this.data('input-id'),
+
+            // Store the DOM/MathJax elements in which visible output occurs.
+            $preview: $preview,
+            // Note: sometimes MathJax hasn't finished loading yet.
+            jax: MathJax.Hub.getAllJax($preview[0])[0],
+            $img: $preview.find("img.loading"),
+
+            requestCallback: null  // Fill it in in a bit.
+        };
+
+        // Give callback access to `inputData` (fill in first parameter).
+        inputData.requestCallback = _.partial(updatePage, inputData);
+
+        // Limit `sendRequest` and have it show the loading icon.
+        var throttledRequest = _.throttle(
+            sendRequest,
+            formulaEquationPreview.minDelay,
+            {leading: false}
+        );
+        // The following acts as a closure of `inputData`.
+        var initializeRequest = function () {
+            // Show the loading icon.
+            inputData.$img.css('visibility', 'visible');
+
+            inputData.isWaitingForRequest = true;
+            throttledRequest(inputData, this.value);
+        };
+
+        $this.on("input", initializeRequest);
+        // send an initial
+        MathJax.Hub.Queue(this, initializeRequest);
+    }
+
+    /**
+     * Fire off a request for a preview of the current value.
+     * Also send along the time it was sent, and store that locally.
+     */
+    function sendRequest(inputData, formula) {
+        // Save the time.
+        var now = Date.now();
+        inputData.lastSent = now;
+        // We're sending it.
+        inputData.isWaitingForRequest = false;
+
+        if (formula) {
+            // Send the request.
+            Problem.inputAjax(
+                inputData.url,
+                inputData.inputId,
+                'preview_formcalc',
+                {"formula" : formula, "request_start" : now},
+                inputData.requestCallback
+            );
+            // ).fail(function () {
+            //     // This is run when ajax call fails.
+            //     // Have an error message and other stuff here?
+            //     inputData.$img.css('visibility', 'hidden');
+            // }); */
+        }
+        else {
+            inputData.requestCallback({
+                preview: '',
+                request_start: now
+            });
+        }
+    }
+
+    /**
+     * Respond to the preview request if need be.
+     * Stop if it is outdated (i.e. a later request arrived back earlier)
+     * Otherwise:
+     * -Refresh the MathJax
+     * -Stop the loading icon if this is the most recent request
+     * -Save which request is visible
+     */
+    function updatePage(inputData, response) {
+        var requestStart = response['request_start'];
+        if (requestStart == inputData.lastSent &&
+            !inputData.isWaitingForRequest) {
+            // Disable icon.
+            inputData.$img.css('visibility', 'hidden');
+        }
+
+        if (requestStart <= inputData.requestVisible) {
+            // This is an old request.
+            return;
+        }
+
+        // Save the value of the last response displayed.
+        inputData.requestVisible = requestStart;
+
+        // Prevent an old error message from showing.
+        if (inputData.errorWaitTimeout != null) {
+            window.clearTimeout(inputData.errorWaitTimeout);
+        }
+
+        function display(latex) {
+            // Load jax if it failed before.
+            if (!inputData.jax) {
+                results = MathJax.Hub.getAllJax(inputData.$preview[0]);
+                if (!results.length) {
+                    console.log("Unable to find MathJax to display");
+                    return;
+                }
+                inputData.jax = results[0];
+            }
+
+            // Set the text as the latex code, and then update the MathJax.
+            MathJax.Hub.Queue(
+                ['Text', inputData.jax, latex],
+                ['Reprocess', inputData.jax]
+            );
+        }
+
+        if (response.error) {
+            inputData.$img.css('visibility', 'visible');
+            inputData.errorWaitTimeout = window.setTimeout(function () {
+                display("\\text{" + response.error + "}");
+                inputData.$img.css('visibility', 'hidden');
+            }, formulaEquationPreview.errorDelay);
+        } else {
+            display(response.preview);
+        }
+    }
+
+    // Invoke the setup method.
+    $('.formulaequationinput input').each(setupInput);
+};
+
+formulaEquationPreview.enable();
diff --git a/rakelib/jasmine.rake b/rakelib/jasmine.rake
index 5a0c4acedc..69dfb71ac4 100644
--- a/rakelib/jasmine.rake
+++ b/rakelib/jasmine.rake
@@ -121,6 +121,7 @@ end
 
 static_js_dirs = Dir["common/lib/*"].select{|lib| File.directory?(lib)}
 static_js_dirs << 'common/static/coffee'
+static_js_dirs << 'common/static/js'
 static_js_dirs.select!{|lib| !Dir["#{lib}/**/spec"].empty?}
 
 static_js_dirs.each do |dir|