edx-platform/xmodule/js/src/video/00_async_process.js

(function(define) {
    define(
        'video/00_async_process.js',
        [],
        function() {
            'use strict';

            /**
 * Provides convenient way to process big amount of data without UI blocking.
 *
 * @param {array} list Array to process.
 * @param {function} process Calls this function on each item in the list.
 * @return {array} Returns a Promise object to observe when all actions of a
 *                 certain type bound to the collection, queued or not, have finished.
 */
            var AsyncProcess = {
                array: function(list, process) {
                    if (!_.isArray(list)) {
                        return $.Deferred().reject().promise();
                    }

                    if (!_.isFunction(process) || !list.length) {
                        return $.Deferred().resolve(list).promise();
                    }

                    var MAX_DELAY = 50, // maximum amount of time that js code should be allowed to run continuously
                        dfd = $.Deferred(),
                        result = [],
                        index = 0,
                        len = list.length;

                    var getCurrentTime = function() {
                        return (new Date()).getTime();
                    };

                    var handler = function() {
                        var start = getCurrentTime();

                        do {
                            result[index] = process(list[index], index);
                            index++;
                        } while (index < len && getCurrentTime() - start < MAX_DELAY);

                        if (index < len) {
                            setTimeout(handler, 25);
                        } else {
                            dfd.resolve(result);
                        }
                    };

                    setTimeout(handler, 25);

                    return dfd.promise();
                }
            };

            return AsyncProcess;
        });
}(RequireJS.define));