javascript - javascript - 在初始化之前引用方法

Question

为什么“write2”有效而“write1”无效？

function Stuff() {
    this.write1 = this.method;
    this.write2 = function() {this.method();}
    this.method = function() {
        alert("testmethod");
    }
}
var stuff = new Stuff;
stuff.write1();

Answer 1

因为第二个this.method在执行匿名函数时进行评估，而第一个创建了一个尚不存在的东西的参考副本。

这可能会让人感到困惑，因为它似乎都write1试图write2使用/引用尚不存在的东西，但是当你声明write2你正在创建一个实际上只复制一个引用this然后执行函数体的闭包时，当this有通过添加修改method

Answer 2

It does not work, because you're referencing this.method before it was declared. Change to:

function Stuff() {

    this.write2 = function() {this.method();}

    // First declare this.method, than this.write1.
    this.method = function() {
        alert("testmethod");
    }
    this.write1 = this.method;
}
var stuff = new Stuff;
stuff.write1();