jQuery UI Resizable alsoResize reverse

By modifying the code jQuery uses to implement the alsoResize option, we can make our own alsoResizeReverse option. Then we can simply use this as follows:

$("#resizable").resizable({
    alsoResizeReverse: ".myframe"
});

The structure of the original alsoResize option has been changed over the various versions of jQuery UI and my original code does not work in the newer versions. I'll give the code for adding this functionality in version 1.8.1 and 1.11.4.

Only a few things had to be changed, such as the obvious renaming alsoResize to alsoResizeReverse and subtracting the delta instead of adding it (what makes the resize reversed). The original alsoResize code starts on line 2200 of version 1.8.1 of jQuery UI and line 7922 of version 1.11.4. You can see the few changes needed here.

To add the alsoResizeReverse functionality, add this to your javascript (This should be put outside of document.ready()):

For newer versions of jQuery UI (example is based on v1.11.4):

$.ui.plugin.add("resizable", "alsoResizeReverse", {

    start: function() {
        var that = $(this).resizable( "instance" ),
            o = that.options;

        $(o.alsoResizeReverse).each(function() {
            var el = $(this);
            el.data("ui-resizable-alsoresizeReverse", {
                width: parseInt(el.width(), 10), height: parseInt(el.height(), 10),
                left: parseInt(el.css("left"), 10), top: parseInt(el.css("top"), 10)
            });
        });
    },

    resize: function(event, ui) {
        var that = $(this).resizable( "instance" ),
            o = that.options,
            os = that.originalSize,
            op = that.originalPosition,
            delta = {
                height: (that.size.height - os.height) || 0,
                width: (that.size.width - os.width) || 0,
                top: (that.position.top - op.top) || 0,
                left: (that.position.left - op.left) || 0
            };

        $(o.alsoResizeReverse).each(function() {
            var el = $(this), start = $(this).data("ui-resizable-alsoresize-reverse"), style = {},
                css = el.parents(ui.originalElement[0]).length ?
                    [ "width", "height" ] :
                    [ "width", "height", "top", "left" ];

            $.each(css, function(i, prop) {
                var sum = (start[prop] || 0) - (delta[prop] || 0);
                if (sum && sum >= 0) {
                    style[prop] = sum || null;
                }
            });

            el.css(style);
        });
    },

    stop: function() {
        $(this).removeData("resizable-alsoresize-reverse");
    }
});

For older version (based on v1.8.1 -- my original answer):

$.ui.plugin.add("resizable", "alsoResizeReverse", {

    start: function(event, ui) {

        var self = $(this).data("resizable"), o = self.options;

        var _store = function(exp) {
            $(exp).each(function() {
                $(this).data("resizable-alsoresize-reverse", {
                    width: parseInt($(this).width(), 10), height: parseInt($(this).height(), 10),
                    left: parseInt($(this).css('left'), 10), top: parseInt($(this).css('top'), 10)
                });
            });
        };

        if (typeof(o.alsoResizeReverse) == 'object' && !o.alsoResizeReverse.parentNode) {
            if (o.alsoResizeReverse.length) { o.alsoResize = o.alsoResizeReverse[0];    _store(o.alsoResizeReverse); }
            else { $.each(o.alsoResizeReverse, function(exp, c) { _store(exp); }); }
        }else{
            _store(o.alsoResizeReverse);
        }
    },

    resize: function(event, ui){
        var self = $(this).data("resizable"), o = self.options, os = self.originalSize, op = self.originalPosition;

        var delta = {
            height: (self.size.height - os.height) || 0, width: (self.size.width - os.width) || 0,
            top: (self.position.top - op.top) || 0, left: (self.position.left - op.left) || 0
        },

        _alsoResizeReverse = function(exp, c) {
            $(exp).each(function() {
                var el = $(this), start = $(this).data("resizable-alsoresize-reverse"), style = {}, css = c && c.length ? c : ['width', 'height', 'top', 'left'];

                $.each(css || ['width', 'height', 'top', 'left'], function(i, prop) {
                    var sum = (start[prop]||0) - (delta[prop]||0); // subtracting instead of adding
                    if (sum && sum >= 0)
                        style[prop] = sum || null;
                });

                //Opera fixing relative position
                if (/relative/.test(el.css('position')) && $.browser.opera) {
                    self._revertToRelativePosition = true;
                    el.css({ position: 'absolute', top: 'auto', left: 'auto' });
                }

                el.css(style);
            });
        };

        if (typeof(o.alsoResizeReverse) == 'object' && !o.alsoResizeReverse.nodeType) {
            $.each(o.alsoResizeReverse, function(exp, c) { _alsoResizeReverse(exp, c); });
        }else{
            _alsoResizeReverse(o.alsoResizeReverse);
        }
    },

    stop: function(event, ui){
        var self = $(this).data("resizable");

        //Opera fixing relative position
        if (self._revertToRelativePosition && $.browser.opera) {
            self._revertToRelativePosition = false;
            el.css({ position: 'relative' });
        }

        $(this).removeData("resizable-alsoresize-reverse");
    }
});

Here's a demo: http://jsfiddle.net/WpgzZ/

I had a problem getting the "Simen Echholt"-code to work with jQuery 1.9.1/jquery-ui (1.10.2), but it worked when I exchanged "$(this).data("resizable")" with "$(this).data("ui-resizable")".