JavaScript ecma6将正常功能更改为箭头功能 [英] JavaScript ecma6 change normal function to arrow function

问题描述

我有代码：

function defineProperty(object, name, callback){
    if(object.prototype){
        Object.defineProperty(object.prototype, name, {"get": callback});
    }
}
defineProperty(String, "isEmpty", function(){return this.length === 0;});

，我使用如下：

console.log("".isEmpty, "abc".isEmpty);

并返回：

true, false

现在，我想将功能更改为这个：

Now, I would like to change function to something like this:

defineProperty(String, "isEmptyWithArrow", () => this.length === 0);

但这个是指Window，我不知道如何更改它。

but "this" refers to Window and I do not know how to change it.

我的小提琴

推荐答案

你不能。这不可能箭头功能中的这个是词法的范围，这是他们的突出特点。但是，您需要动态绑定这个，这就是函数是有益的。

You cannot. This impossible. this in arrow functions is lexically scoped, that's their outstanding feature. But you need a dynamically bound this, and that's what functions are good for.

如果您坚持使用新颖的ES6功能，请执行方法定义：

If you insist on using fancy new ES6 features, go for a method definition:

function defineProperty(object, name, descriptor) {
    if (object.prototype)
        Object.defineProperty(object.prototype, name, descriptor);
}
defineProperty(String, "isEmpty", {get(){return this.length === 0;}, configurable:true});

当然，您也可以采取一个回调方式，获取实例作为参数：

Of course, you could also take a callback that gets the instance as an argument:

function defineProperty(object, name, callback) {
    if (object.prototype)
        Object.defineProperty(object.prototype, name, {
            get(){ return callback(this); }, // dynamic this
            configurable: true
        });
}
defineProperty(String, "isEmpty", self => self.length === 0);

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