为什么jQuery的承诺有一个done（），但是Mozilla记录的Javascript承诺不是？如果我想在JS中有一个done（）怎么办？ [英] Why does jQuery's promise have a done(), but Javascript's promise documented by Mozilla does not? What if I want to have a done() in JS?

问题描述

Mozilla的JavaScript文档'Promises之间有什么区别（参见 API页面）和jQuery的Promises（参见 API页面）？

What are the differences between Mozilla's JavaScript docs' Promises (see API page) and jQuery's Promises (see API page)?

Mozilla的承诺似乎只有两种方法：然后赶上。 jQuery的承诺似乎有更多的方法，包括：then，done和fail。 （从这里开始）

Mozilla's promise seems to have only 2 methods: then and catch. jQuery's promise seems to have more methods, including: then, done, and fail. (from here)

为什么Mozilla上的JS API没有 done（）？如果我想在JavaScript中使用done（）功能怎么办？我该怎么办？

How come the JS API on Mozilla doesn't have done()? What if I want to have a done() functionality in JavaScript? What do I do?

推荐答案

jQuery的延迟API 是膨胀的，早于承诺库。一旦他们意识到承诺有多么有用，他们就添加了然后（或以前， pipe ）方法，但是他们未能100％正确。

jQuery's deferred API is bloated and predates promise libraries. Once they realised how useful promises were, they added a then (or previosly, pipe) method, however it they failed to get it 100% right.

为什么Mozilla上的JS API没有 done（）？

完全没必要。所有 Promises / A +兼容实施（包括ES6）只需要一种方法：。然后（）。它完全是通用的，你可以用它做任何事情 - 这是承诺的原始。

It's completely unnecessary. All Promises/A+ compatible implementations (which includes ES6) only need a single method: .then(). It's completely universal, you can do everything with it - it's the primitive of promises.

如果我想在JavaScript中使用 done（）功能怎么办？我该怎么办？

What if I want to have a done() functionality in JavaScript? What do I do?

好吧，你可以自己实现它：

Well, you could implement it yourself:

Promise.prototype.done = function(cb) { // or function(...cbs) for (let cb of cbs) …
    this.then(cb).then(null, function(err) { /* ignore */ });
    return this;
};

但是从中可以看出，它实际上并不是很有用。它没有链，它忽略了异常，所以你应该只使用然后无处不在。

But as you can see from that, it's not very useful actually. It doesn't chain, and it ignores exceptions, so you should just use then everywhere.

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