Fix jQuery and DOM-related Memory Leaks in IE < 9

ie-memory-fix.js

/**
 * Fix JS/DOM memory leaks in IE < 9.
 * Tested w/ jQuery 1.8.2, but should be compatible w/ jQuery 1.7.x
 */
(function( $, undefined ) {
    /**
     * <code>true</code> if the browser is IE &lt; 9; otherwise <code>false</code>
     * @type {Boolean}
     */
    var oldIE = $('<span/>').html('<!--[if lt IE 9 ]><div></div><![endif]-->').find('div').length > 0;

    /**
     * Standard DOM events and expando properties
     * {
     *     expandoProp: [ elem1, elem2, ... ],
     *     onclick:     [ elem3, elem4, ... ],
     *     ondragstart: [ elem5, elem6, ... ]
     * }
    */
    var domProps = {};

    /**
     * Sets the value of a DOM element property, making sure that it gets cleaned up when the page unloads.
     * @param {HTMLElement} elem DOM element
     * @param {String} eventName name of the event (e.g., "ondragstart")
     * @param {Function} fn event handler
     */
    $.register = function(elem, eventName, fn) {
        domEvents[eventName] = domEvents[eventName] || [];
        domEvents[eventName].push(elem);
        elem[eventName] = fn;
    };


    // Don't bother fixing memory leaks in modern browsers
    if ( ! oldIE ) return;


    /*
     * jQuery event handlers
     * (e.g., $(elem).on('click', function() { ... }))
     */


    var jqEvents = {
        on: [ /* $elem1, $elem2, ... */ ],
        bind: [ /* $elem1, $elem2, ... */ ]
    };

    var ron = /^on/;

    /**
     * Map of fully-qualified custom event names (w/ the "on" prefix - e.g., "ontrySubmit")
     * (NOTE: Values must be "truthy" to allow lookup expressions to evaluate to true,
     *        but are otherwise meaningless.)
     */
    var customEventNames = { /* oninit: true, ontrySubmit: true, ... */ };

    /**
     * Map of standard DOM level 2-3 events to skip when removing global events.
     * (NOTE: Values must be "truthy" to allow lookup expressions to evaluate to true,
     *        but are otherwise meaningless.)
     */
    var domEventNames = { onunload: true, onbeforeunload: true };

    /**
     * Returns an array containing the names of all non-inherited properties of an object.
     * @param {Object} hash
     * @return {Array}
     */
    function keys(hash) {
        var arr = [];
        $.each(hash, function(key) { arr.push(key); });
        return arr;
    }

    /**
     * Returns the normalized name of a jQuery event string (including the 'on' prefix).
     *
     * @example <code>normalizeJqEventName('click') == 'onclick'</code>
     * @example <code>normalizeJqEventName('onclick') == 'onclick'</code>
     * @example <code>normalizeJqEventName('click.namespace') == 'onclick'</code>
     * @example <code>normalizeJqEventName('.namespace') == null</code>
     *
     * @param {String} jqEventName e.g., <code>"click.namespace"</code>
     * @return {String} the normalized name of the event (e.g., <code>"onclick"</code>) or <code>null</code> if none is present
     */
    function normalizeJqEventName(jqEventName) {
        var idx = jqEventName.indexOf('.');
        var eventName = idx > -1 ? jqEventName.substring(0, idx) : jqEventName;

        // Remove element from array in $.map()
        if (!eventName)
            return null;
        // Make sure event name starts with "on"
        else
            return ron.test(eventName) ? eventName : 'on' + eventName;
    }

    /**
     * Registers non-standard DOM events so that they can be removed on page unload.
     * @param {String|Object} events a string or map of jQuery event name(s)
     */
    function addCustomEventHandler(events) {
        if ( typeof events === 'string' ) {
            events = events.split(/\s+/g);
        } else {
            events = keys(events);
        }
        $.each($.map(events, normalizeJqEventName), function(i, eventName) {
            // Skip standard DOM events (e.g., "onclick")
            if (!domEventNames[eventName]) {
                customEventNames[eventName] = true;
            }
        });
    }

    /**
     * Removes custom DOM events from an element so they don't leak memory in IE &lt; 9.
     * @param {jQuery} $elem
     */
    function clearCustomEventHandlers($elem) {
        $elem.each(function() {
            var elem = this;
            $.each(customEventNames, function(eventName) {
                elem[eventName] = null;
            });
            elem = null;
        });
        $elem = null;
    }


    var supr = {
        on: $.fn.on,
        off: $.fn.off,
        bind: $.fn.bind,
        unbind: $.fn.unbind
    };


    $.fn.extend({

        on: function (events) {
            var result = supr.on.apply(this, arguments);
            jqEvents.on.push(this);
            addCustomEventHandler(events);
            return result;
        },

        bind: function (events) {
            var result = supr.bind.apply(this, arguments);
            jqEvents.bind.push(this);
            addCustomEventHandler(events);
            return result;
        },

        off: function () {
            var result = supr.off.apply(this, arguments);
            clearCustomEventHandlers(this);
            return result;
        },

        unbind: function () {
            var result = supr.unbind.apply(this, arguments);
            clearCustomEventHandlers(this);
            return result;
        }

    });


    var onunload = function() {
        var i;

        for (i = 0; i < jqEvents.on.length; i++) {
            jqEvents.on[i].off();
        }

        for (i = 0; i < jqEvents.bind.length; i++) {
            jqEvents.bind[i].unbind();
        }

        jqEvents.on = [];
        jqEvents.bind = [];

        for (var propertyName in domProps) {
            if (domProps.hasOwnProperty(propertyName)) {
                var elems = domProps[propertyName];
                for (i = 0; i < elems.length; i++) {
                    elems[i][propertyName] = null;
                }
            }
        }

        domProps = {};
    };

    $(window).on("unload", function() {
        try {
            onunload();
        }
        catch(e) {}
        finally {
            domProps = jqEvents = onunload = null;
        }
    });

})( jQuery );