js绑定事件this指向发生改变的问题解决方法

Function.prototype.bind = function(obj) { 
var _this = this; 
return function() { 
_this.apply(obj,arguments); 
} 
}

var a = function(){ 
alert(this.title) 
}.bind(document); 
a();

function myalert() { 
this.title = 'hello world'; 
this.init = function() { 
$("#xxx").click(this.close.bind(this)); 
} 
this.close = function() { 
alert(this.title) 
} 
}

<P style="PADDING-BOTTOM: 0px; LINE-HEIGHT: 22px; MARGIN-TOP: 0px; FONT-FAMILY: 微软雅黑, 宋体, 'Trebuchet MS', Tahoma, Arial, sans-serif; MARGIN-BOTTOM: 10px; COLOR: rgb(34,34,34); FONT-SIZE: 14px; PADDING-TOP: 0px" class=p1>var a  = new myalert();</P><P style="PADDING-BOTTOM: 0px; LINE-HEIGHT: 22px; MARGIN-TOP: 0px; FONT-FAMILY: 微软雅黑, 宋体, 'Trebuchet MS', Tahoma, Arial, sans-serif; MARGIN-BOTTOM: 10px; COLOR: rgb(34,34,34); FONT-SIZE: 14px; PADDING-TOP: 0px" class=p1>a.init();</P>