javascript - NodeJS 对象内的匿名函数

Question

为什么以下代码不返回“a 和 b”？

Staff.config = {
    a: 'a constant',
    b: (function(){
        return this.a + ' and b';
    })()
};

console.log(Staff.config) // { a: 'a constant', b: 'undefined and b' }

Answer 1

(function(){ return this.a + ' and b'; })() is getting executed under the global scope(this refers to window in browser) and in your case, global context does not have property a hence it is undefined.

更简单的解决方案是使用函数表达式作为b的值，因此Staff.config.b()将返回预期的输出。

var Staff = {};
Staff.config = {
  a: 'a constant',
  b: function() {
    return this.a + ' and b';
  }
};
alert(Staff.config.b());

You could achieve the same using getter which gets the value of a specific property

试试这个:

var Staff = {};
Staff.config = {
  a: 'a constant',
  get b() {
    return this.a + ' and b';
  }
};
alert(Staff.config.b);