new 关键字 return funciton 问题

Question

function people(word){    this.word = word;    this.say = function(){      console.log(this.word);    }    this.capacity = function(){      return this.say;    }  }  var p = new people('Hello World');  var res = p.capacity();  console.log(res)//ƒ (){console.log(this.word);}  console.log(res())//undefined如上带吗,我new了一个people,返回的res 是一个function但是为什么 我执行这个res为undefined,求解,我想的应该打印出来 hello world如果改成这样呢function people(word){this.word = word;this.say = function(){  console.log(this.word);}()this.capacity = function(){  return this.say;}}var p = new people('Hello World');var res = p.capacity(); //undefined为什么res是undefined

Answer 1

好像回答的很晚。你return一个this.say，而this.say在this.capacity中构成了一个嵌套函数，而在js里嵌套函数中this是指向window，window中没有window.word,所以为undefined。

我认为把this保存在that里即可：

function people(word){

        var that=this;

        this.word = word;

        this.say = function(){

        console.log(that.word);

    }

        this.capacity = function(){

        return this.say;

    }

  }