javascript 中 this 的指向

在函数中 this 指向 window

(function whatThis() {  console.log(this);})()

输出结果：
Window {speechSynthesis: SpeechSynthesis, caches: CacheStorage, localStorage: Storage, sessionStorage: Storage, webkitStorageInfo: DeprecatedStorageInfo…}

在方法中 this 指向 调用方法的对象

var object = {  getThis: function() {    console.log(this);  }}object.getThis();

输出结果：

1. Object {}
   1. getThis:()
      1. arguments:null
      2. caller:null
      3. length:0
      4. name:"getThis"
      5. prototype:Object
      6. __proto__:()
      7. <function scope>
   2. __proto__:Object

在构造函数的实例中，this 指向 new 出的实例

var GetThis = function() {  console.log(this);}var testThis = new GetThis();

输出结果：

1. GetThis {}
   1. __proto__:Object
      1. constructor:()
      2. __proto__:Object

在apply中，this 指向传入的对象

var GetThis = function(str) {}GetThis.prototype.getString = function() {  console.log(this);}var obj = {str: "I can't guess this!"};GetThis.prototype.getString.apply(obj);

输出：

1. Object {str: "I can't guess this!"}
   1. str:"I can't guess this!"
   2. __proto__:Object

参考：道格拉斯的语言精粹