javascript - js原型小问题

问题描述

问 题

function Tt(){
    this.name = "hello";
    this.age = 88;
    if(typeof this.say != "function"){
        Tt.prototype = {
            constructor: Tt,
            say: function(){
                return this.name;
            }
        };
    }
}
var t = new Tt();
**console.log(t.say());   // Uncaught TypeError: Object #<Tt> has no method 'say'  这里为什么访问不到方法？？？**


// 如果这么做
function Tt(){
    this.name = "hello";
    this.age = 88;
    if(typeof this.say != "function"){
        Tt.prototype.say = function(){
                return this.name;
            }
    }
}
var t = new Tt();
**console.log(t.say()); // 这样就没有问题！**

小白，不知道为什么这样？？希望帮忙解释一下~

解决方案

What happens when a constructor is called? When new Vehicle() is called, JavaScript does four things:

• It creates a new object.

• It sets the constructor property of the object to Vehicle.

• It sets up the object to delegate to Vehicle.prototype.

• It calls Vehicle() in the context of the new object.

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