有什么理由在构造函数中手动`return'？

问题描述

通常，在构造函数中，在函数中 this 绑定的对象在使用 new 前缀。但我想象，也有可能（我想我甚至在crockford的书中阅读）手动返回您自己的值。

解决方案

如果你从构造函数返回一个值类型，你会得到不同的行为取决于是否使用 new 。这就是 String 的工作原理。在您的JavaScript控制台中查看此对象：

  {
s：String（abc），
 S：new String（abc）
} 
  

Little s 包含字符串值，但大 S 包含字符串Object。

<$>

<$>

p $ p> function Foo（）{
returnabc;
}
Foo.prototype.DoSomething = function（）{
//与abc完全无关的
};
var a = Foo（）; //字符串abc。没有DoSomething（）方法。
var b = new Foo（）; //具有DoSomething（）方法的对象。不知道abc。


根据是否使用 new 得到完全不同的东西。

Typically, in a constructor function, the object that is bound to this within the function is returned by it when it is called with the new prefix. But I would imagine that it's also possible (I think I even read this in crockford's book) to manually return your own value. Are there any places where such a practice is useful?

解决方案

If you return a value type from the constructor, you'll get different behavior depending on if new was used. That's how String works. Look at this object in your JavaScript console:

{
    s: String("abc"),
    S: new String("abc")
}

Little s contains a string value, but big S contains a string Object. A subtle difference, perhaps.

You could go way beyond that and use the same function for different purposes:

function Foo() {
    return "abc";
}
Foo.prototype.DoSomething = function () {
    // something completely unrelated to "abc"
};
var a = Foo();      // The string "abc".  Does not have a DoSomething() method.
var b = new Foo();  // An Object with a DoSomething() method.  Doesn't know about "abc".

Depending on whether new was used, you'd get back something completely different.

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