个人对JQuery Proxy()函数的理解

转载至：http://www.cnblogs.com/acles/archive/2012/11/20/2779282.html

JQuery.proxy(function,context):

使用context代替function中的context。

比如：

var you = {

  type: "person",

  test: function(event) {

    $("#log").append( this.type + " " );

  }

$("#test").click(you.test);调用这句只有相当于调用：

$("#test").click(function(event){

         $("#log").append( this.type + " " );

});

所以这里的this指的是$("#test").

如果这样调用：$("#test").click($.proxy(you.test,you));

此时的调用相当于：

$("#test").click(function(event){

$("#log").append( you.type + " " );

});

虽然调用事件的对象是$("#test")，但是却可以使用$.proxy把事件执行内的对象改变为you。

JQuery.proxy(context,functionname):

第一个参数是你想proxy的对象，第二个参数为要改变的函数的名字。

var obj = {

name: "John",

test: function() {

$("#log").append( this.name );

$("#test").unbind("click", obj.test);

}

};

$("#test").click( jQuery.proxy( obj, "test" ) );   把obj作为context传入test中，而不是$("#test").

这个执行完之后，结果会是John，

如果使用下面这句

$("#test").click(obj.test);

结果会是$("#test").的name值。

这个函数和上面的那个函数的功能一样，就是使用了更加简洁的方式。

最后附上一篇stackoverflow的一个关于Porxy的一个问答的答案。问答原地址：http://stackoverflow.com/questions/4986329/understanding-proxy-in-jquery

What it ultimately does is it ensures that the value of this in a function will be the value you desire.

A common example is in a setTimeout that takes place inside a click handler.

Take this:

$('#myElement').click(function() {

        // In this function, "this" is our DOM element.

    $(this).addClass('aNewClass');

});

The intention is simple enough. When myElement is clicked, it should get the class aNewClass. Inside the handler this represents the element that was clicked.

But what if we wanted a short delay before adding the class? We might use a setTimeout to accomplish it, but the trouble is that whatever function we give to setTimeout, the value of thisinside that function will be window instead of our element.

$('#myElement').click(function() {

    setTimeout(function() {

          // Problem! In this function "this" is not our element!

        $(this).addClass('aNewClass');

    }, 1000);

});

So what we can do instead, is to call $.proxy(), sending it the function and the value we want to assign to this, and it will return a function that will retain that value.

$('#myElement').click(function() {

   // ------------------v--------give $.proxy our function,

    setTimeout($.proxy(function() {

        $(this).addClass('aNewClass');  // Now "this" is again our element

    }, this), 1000);

   // ---^--------------and tell it that we want our DOM element to be the

   //                      value of "this" in the function

});

So after we gave $.proxy() the function, and the value we want for this, it returned a function that will ensure that this is properly set.

How does it do it? It just returns an anonymous function that calls our function using the .apply()method, which lets it explicitly set the value of this.

A simplified look at the function that is returned may look like:

function() {

    // v--------func is the function we gave to $.proxy

    func.apply( ctx );

    // ----------^------ ctx is the value we wanted for "this" (our DOM element)

}

So this anonymous function is given to setTimeout, and all it does is execute our original function with the proper this context.