proxy : 改变this指向
使用方法1：
function show(){
alert(this);
}
$.proxy(show,document)(); //document
使用方法2：
function show(n1,n2){
alert(n1);
alert(n2);
alert(this);
}
$.proxy(show,document)(3,4); //document 3 4
$.proxy(show,document,3,4)(); //document 3 4
$.proxy(show,document,3)(4); //document 3 4
使用方法3：
var obj = {
show:function(){
alert(this);
}
};
$(document).click($.proxy(obj,'show')); //object
从proxy方法的源码可以看出，以下代码片段是针对 ' 使用方法3 ' 做了处理，它允许第二个参数为字符串，其实等同于：$(document).click($.proxy(obj.show,obj));
if ( typeof context === "string" ) {
tmp = fn[ context ];
context = fn;
fn = tmp;
}
以下代码片段是针对传参的处理，先使用core_slice.call截取第3个参数到最后，再获取调用时的参数，最后合并。
// Simulated bind
args = core_slice.call( arguments, 2 );
proxy = function() {
return fn.apply( context, args.concat( core_slice.call( arguments ) ) );
};
proxy完整的代码：
var core_slice = Array.prototype.slice,
....................
jQuery.extend({
......................
// A global GUID counter for objects
guid: 1,
// Bind a function to a context, optionally partially applying any
// arguments.
proxy: function( fn, context ) {
var tmp, args, proxy;
if ( typeof context === "string" ) {
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
args = core_slice.call( arguments, 2 );
proxy = function() {
return fn.apply( context, args.concat( core_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 || jQuery.guid++;
return proxy;
},
...............
});