将对象分配给“this” [英] Assign object to "this"

问题描述

假设我有一个类和一些静态辅助方法，如下所示：

Say I have a class and some static helper methods like this:

function MyClass (myVar) {
    this.myVar = myVar;

    this.replaceMe = function (value) {
        // this will fail
        this = MyClass.staticHelper( value );

        return this;
    }

    this.revealVar = function () {
        alert( this.myVar );
    }
}

MyClass.staticHelper = function (instance, value) {
    return new MyClass( instance.myVar + value );
}

我想做的是这样的事情：

What I want to do is something like this:

var instance = new MyClass( 2 );

instance.revealVar(); // alerts 2
instance.replaceMe( 40 ).revealVar(); // alerts 42

原因是我的课程结构稍微复杂一点，我不知道想要每次手动分配所有内部变量，而是替换整个对象。有一个简单的方法吗？

The reason is that my class has a slightly more complicated structure and I don't want to assign all internal variables manually everytime, but rather replace the entire object. Is there a simple way to do so?

推荐答案

instance.replaceMe （40）.revealVar（）; 提醒42

好的，对于返回MyClass.staticHelper（this，value）; 就足够了。问题只是下一次调用 instance.revealVar（）现在是否应该警告2或42 - 如果你想要实例要改为42，它会变得更复杂：

OK, for that return MyClass.staticHelper(this, value); would suffice. The question is only whether the next call to instance.revealVar() should now alert 2 or 42 - if you want instance to be changed to 42 it gets more complicated:

this = MyClass.staticHelper( value ); // this will fail

...因为 此 不是常见变量，而是 keyword 和 计算当前执行上下文的ThisBinding的值 根据输入功能的方式设置 - 您不能分配给它，你只能在调用函数时设置它。

…because this is not a common variable, but a keyword and evaluates to the value of the ThisBinding of the current execution context which is set depending on how the function is entered - you cannot assign to it, you can only set it when invoking the function.

我不希望每次手动分配所有内部变量，而是替换整个对象。

I don't want to assign all internal variables manually everytime, but rather replace the entire object.

不幸的是，您必须这样做，而不更改 instance <的属性/ code> object（和闭包隐藏变量）你不会改变实例和 revealVar（）将st ay 2.

Unfortunately you have to do so, without changing the properties of instance object (and the closure-hidden variables) you won't change the instance and revealVar() will stay 2.

有一种简单的方法吗？

Is there a simple way to do so?

是的，它可以通过编程方式完成。最简单的方法是致电构造函数（再次） on 当前实例，就像使用 新的关键字：

Yes, it can be done programmatically. The simplest method would be to call the constructor (again) on the current instance, like it happens when invoked with the new keyword:

MyClass.call( instance, instance.myVar + value );

然而，你不能像创建一个全新实例的静态函数那样使用它。你把它放在一个静态的方法，然后用 replaceMe 用这个调用它，或者你直接把它放在 replaceMe 。

Yet you can't use this like the static function which creates a completely new instance. Either you put it in a static method and call that from replaceMe with this, or you just put it directly in replaceMe.

如果你需要一个静态方法，它首先返回一个全新的实例，你也可以使用它通过复制旧实例上的新属性：

If you need a static method that at first returns a completely new instance, you could use that as well by copying the new properties on the old instance:

….replaceMe = function(val) {
    var newInst = MyClass.staticHelper(this, val); // new MyClass(this.myVar+val);
    for (var prop in newInst)
        if (newInst.hasOwnProperty(prop))
            this[prop] = newInst[prop];
    return this;
};

这意味着要覆盖旧属性，而且旧的闭包现在可以被垃圾收集，因为没有引用再给他们了。

That means overwriting the old attributes, and also the old closures can be garbage-collected now as nothing refers to them any more.

顺便说一句，我建议将你的方法放在原型上，而不是在构造函数中分配它们。

Btw, I'd recommend to put your methods on the prototype instead of assigning them in the constructor.

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