Question

In jQuery API doc, the jQuery.proxy function usage:

jQuery.proxy( function, context )

---

function The function whose context will be changed.
context The object to which the context (this) of the function should be set.

jQuery.proxy( context, name )

---

context The object to which the context of the function should be set.
name The name of the function whose context will be changed (should be a property of the context object).

proxy : function(fn, proxy, thisObject){
    if ( arguments.length === 2 ) {
        if (typeof proxy === "string" ) {
        thisObject = fn;
        fn = thisObject[proxy];
        proxy = undefined;
    } else if ( proxy && !jQuery.isFunction( proxy ) ) {
        thisObject = proxy;
        proxy = undefined;
    }
}
   if ( !proxy && fn ) {
   proxy = function() {
   return fn.apply( thisObject || this, arguments );
   };
}
// So proxy can be declared as an argument
return proxy;
}

But when I look into jQuery source code, of function proxy. I found there’re 3 parameters declared.

So I wonder what’s the use of third param, cannot understand the code 🙁

I write a code segment to test the function.

var someObj = { somefnc : function() {} };
function fnc() {
    this.somefnc();
    console.log(arguments);
}
var proxyedFnc = jQuery.proxy(fnc, undefined, someObj, "arg1","arg2");
proxyedFnc();
//output: []

And I wonder why the arguments were not passed to fnc..

Answer 1

Below is the source comes from jquery-1.7.2.js, Are you sure you check the same version between source and api doc?

// Bind a function to a context, optionally partially applying any
// arguments.
proxy: function( fn, context ) {
    if ( typeof context === "string" ) {
        var tmp = fn[ context ];
        context = fn;
        fn = tmp;
    }

    // Quick check to determine if target is callable, in the spec
    // this throws a TypeError, but we will just return undefined.
    if ( !jQuery.isFunction( fn ) ) {
        return undefined;
    }

    // Simulated bind
    var args = slice.call( arguments, 2 ),
        proxy = function() {
            return fn.apply( context, args.concat( slice.call( arguments ) ) );
        };

    // Set the guid of unique handler to the same of original handler, so it can be removed
    proxy.guid = fn.guid = fn.guid || proxy.guid || jQuery.guid++;

    return proxy;
},