Make Forwarding Object

Makes a forwarding object that forwards all functions calls and attribute requests to the forwarded object. In this way, the original object is acted upon directly, while you can delete or modify members to your object without interfering with the original. Access to the object being forwarded to is always available using member functions applyParent(), callParent(), setParentAttrib() and getParentAttrib(). If funcs or attribs are enumerable in the object, they are not added a second time.

by Adrian

HTML

<canvas id='myCanvas' width='100' height='100' style='
                position:absolute
                z-index:0;
                left:0px;
                top:0px;
                pointer-events:none;
                border:1px solid;' />

JavaScript

// makeForwardingObject(obj, funcs, attribs)
//
//        obj - the object that is being forwarded to
//      funcs - array of non enumerable function member names to forward to
//    attribs - array of non enumerable attributes to forward to
//
// Makes a forwarding object that forwards all functions calls and attribute
// requests to the forwarded object.  In this way, the original object is
// acted upon directly, while you can delete or modify members to your 
// object without interfering with the original.
//
// Access to the object being forwarded to is always available using member
// functions applyParent(), callParent(), setParentAttrib() and 
// getParentAttrib().
//
// If funcs or attribs are enumerable in the object, they are not added 
// a second time.
function makeForwardingObject(obj, funcs, attribs)
{
    var _ = { };
    Object.defineProperties(_, {
        _: { value: obj },
        // like obj.apply() except it applys to object being forwarded to.
        applyParent : { value: function applyParent(func, args)
        {
            return this._[func].apply(this._, args);
        }},
        // like obj.call() except it applys to object being forwarded to.
        callParent: { value: function callParent(func)
        {
            // FF at least doesn't understand arguments.slice(), 
            // arguments.splice() or arguments.shift().  WTF?!?!
            var args=[];
            for (i=1; i<arguments.length; ++i)
                args[i-1]=arguments[i];
            return this._[func].apply(this._, args);
        }},
        // this is for setting member of object being forwarded to.
        setParentAttrib: { value: function setParentAttrib(attrib, val)
        {
            return this._[attrib]=val;
        }},
        // this is for getting member of object being forwarded to.
        getParentAttrib: { value: function getParentAttrib(attrib, val)
        {
            return this._[attrib];
        }},
    });
    
    for (var key...