为什么 Javascript 构造函数没有 return

Question

我有问题。当我从一个对象实例化时，它不会 return 构造函数的值。 ..................................................... ..................................................... ..................................................... ………… ..................................................... ..................................................... ..................................................... ..........

//Main Branch
var Creatures = function () {
    function Creatures(name,alive) {
        this.name = name;
        this.alive = alive;
    }
    function Creatuers(name,alive,sleep) {
        this.name = name;
        this.alive = alive;
        this.sleep = sleep;
    }
};

var Beast = function () {
    function breathe() {
        return true;
    }
    this.__proto__ = new Creatures;
};
var Mammals = function () {
    this.numberOfBeads = "i am numberOfBeads from Mammals";
    this.__proto__ = new Beast;
};


//Mammals Branch
var Humans = function () {
    function thinking(){
        return true;
    }
    this.love = "i am love from humans";
    this.__proto__ = new Mammals;
};
var Animals = function () {
    this.instinct = "i am Animals from Animals";
    this.__proto__ = new Mammals;
};
var Plants = function () {
    this.color = "i am color from Plants";
    function grown() {
        return true;
    }
    this.__proto__ = new Creatures;
};
var Trees = function () {
    this.height = "i am height from Trees";
    this.__proto__ = new Plants;
};
var Flowers = function () {
    this.smell = "i am smell from Flowers";
    this.__proto__ = new Plants;
};
var Grasses = function () {
    this.color = "i am color from Grasses";
    this.__proto__ = new Plants;
};
var obj2 = new Creatures("ali",true);
alert(obj2.name);

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Index</title>
</head>
<body>

<script src="sampleObject1.js"></script>
<script src="sampleObject2.js"></script>
</body>
</html>

Answer 1

正如@Denys Seguret 所说，我可以确认，某些事情似乎相当晦涩...

无论如何，你得到 undefined 因为函数构造函数 return 一个具有你在该函数构造函数中附加的属性的对象。

在你的例子中，你的函数是：

var Creatures = function () {
    function Creatures(name,alive) {
        this.name = name;
        this.alive = alive;
    }
    function Creatures(name,alive,sleep) {
        this.name = name;
        this.alive = alive;
        this.sleep = sleep;
    }
};

这是一个函数表达式，在其作用域内有两个同名函数（第二个将覆盖第一个，尽管第一个没用）。

如您所见，您没有为将从中隐式 return 编辑的对象设置任何类型的属性。

我让你的例子工作只是用第二个函数声明替换它：

function Creatures(name,alive,sleep) {
  this.name = name;
  this.alive = alive;
  this.sleep = sleep;
}

var obj2 = new Creatures("ali", true);
alert(obj2.name);

这会发出一个提示 "ali"。

Answer 2

函数中没有任何 return 语句

var Creatures = function () {
    function Creatures(name,alive) {
        this.name = name;
        this.alive = alive;
    }
    function Creatuers(name,alive,sleep) {
        this.name = name;
        this.alive = alive;
        this.sleep = sleep;
    }
};

您可能想要做的是委托对象的实例化，根据参数（可能还有一些业务逻辑）选择合适的构造函数。请注意 javascript 中没有方法重载，因此您需要为内部函数使用不同的命名。

var Creatures = function (...params) {
    function Creatures1(name,alive) {
        this.name = name;
        this.alive = alive;
    }
    function Creatures2(name,alive,sleep) {
        this.name = name;
        this.alive = alive;
        this.sleep = sleep;
    }
    return params.length === 2 ? new Creatures1(...params) : new Creatures2(...params);
};

var obj2 = Creatures("ali",true);
alert(obj2.name);

Answer 3

如果你指的是 var obj2 = new Creatures("ali",true);它有return一个实例！它不会 return 具有属性 name 和 alive 的新 Creatures 实例，因为这些不是构造函数的参数，也不是构造函数中设置的属性 (top -一级):

var Creatures = function () {
    ...
};

您似乎想做的是创建重载的构造函数？！ javascript!

不支持函数重载

为什么 Javascript 构造函数没有 return

Why Javascript constructor doesn't return

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