var name = "pig";
function Person(name){
  this.name = name;
  this.getName = function(){
    setTimeout(function(){
      console.log("Hello,my name is "+this.name);
    },100);
  }
}
var weiqi = new Person("卫旗");
weiqi.getName();  
//Hello,my name is pig

var name = "pig";
function Person(name){
  this.name = name;
  this.getName = function(){
    //在这里缓存一个this
    var self = this;
    setTimeout(function(){
      //在这里是有缓存this的self
      console.log("Hello,my name is "+self.name);
    },100);
  }
}
var weiqi = new Person("卫旗");
weiqi.getName();
//Hello,my name is 卫旗

var name = "pig";
function Person(name){
  this.name = name;
  this.getName = function(){
    setTimeout(function(){
      console.log("Hello,my name is "+this.name);
    }.bind(this),100);
    //注意上面这一行，添加了bind(this)
  }
}
var weiqi = new Person("卫旗");
weiqi.getName();
//Hello,my name is 卫旗

//定义全局变量x
var x = "window";
//在module内部定义x
var module = {
  x:"module",
  getX:function(){
    console.log(this.x);
  }
}
module.getX(); 
//返回module，因为在module内部调用getX()

var getX = module.getX;
getX();
//返回window，因为这个getX()是在全局作用域中调用的

//绑定getX()并将this值设为module
var boundGetX = getX.bind(module);
boundGetX();
//返回module，绑定以后this值始终为module

if (!Function.prototype.bind) {
 Function.prototype.bind = function (oThis) {
  if (typeof this !== "function") {
   // closest thing possible to the ECMAScript 5 internal IsCallable function
   throw new TypeError("Function.prototype.bind - what is trying to be bound is not callable");
  }

  var aArgs = Array.prototype.slice.call(arguments, 1), 
    fToBind = this, 
    fNOP = function () {},
    fBound = function () {
     return fToBind.apply(this instanceof fNOP && oThis
                 ? this
                 : oThis || window,
                aArgs.concat(Array.prototype.slice.call(arguments)));
    };

  fNOP.prototype = this.prototype;
  fBound.prototype = new fNOP();

  return fBound;
 };
}

    fun.bind(thisArg[, arg1[, arg2[, …]]])