p Promises are useful both in node.js and the browser. We immediately have a resolved promise.A Promise object serves as a link between the executor (the “producing code” or “singer”) and the consuming functions (the “fans”), which will receive the result or error.

Output: Success, You are a GEEK; Promise Consumers. ES6 原生提供了 Promise 对象。 所谓 Promise，就是一个对象，用来传递异步操作的消息。它代表了某个未来才会知道结果的事件（通常是一个异步操作），并且这个事件提供统一的 API，可供进一步处理。 Promise 对象有以下两个特点。 （1）对象的状态不受外界影响。Promise 对象代表一个异步操作，有三种状态：Pending（进行中）、Resolved（已完成，又称 Fulfilled）和 Rejected（已失败）。只有异步操作的结果，可以决定当前是哪一种状态，任何其他操作都无法改变这个状态。这也是 Promise 这个名字的 … Consuming functions can be registered (subscribed) using methods For instance, here’s a reaction to a successfully resolved promise:If we’re interested only in successful completions, then we can provide only one function argument to If we’re interested only in errors, then we can use And here there’s an error in the promise, passed through We’ll talk more about promise chaining and result-passing between handlers in the next chapter.Note that this is different, and more powerful than the real life “subscription list” scenario. : We must have a callback function at our disposal when calling loadScript(script, callback).In other words, we must know what to do with the result before loadScript is called.

Upon provision of an initial promise, a chain of promises can follow. To force more errors, change the The fulfillment of the promise is simply logged, via a fulfill callback set using This example is started by clicking the button.

Any termination other than a The promises of a chain are nested like Russian dolls, but get popped like the top of a stack. But there’s more. На promise можно навешивать колбэки двух типов: onFulfilled – срабатывают, когда promise в состоянии «выполнен успешно». A Promise object is created using the new keyword and its constructor.

jQuery. The effect is much like that of This example shows diverse techniques for using Promise capabilities, and diverse situations that can occur.

We can add handlers any time: if the result is already there, our handlers get it immediately.Next, let’s see more practical examples of how promises can help us write asynchronous code.Here’s the callback-based variant, just to remind us of it:We can immediately see a few benefits over the callback-based pattern:So promises give us better code flow and flexibility.

jQuery's promises have a poorly thought out API that will likely just confuse you.

First, we run loadScript(script), and .then we write what to do with the result. For the following code, the transiton of An action can be assigned to an already "settled" promise. The JavaScript promises API will treat anything with a then() method as promise-like (or thenable in promise-speak sigh), so if you use a library that returns a Q promise, that's fine, it'll play nice with the new JavaScript promises. In that case the action (if appropriate) will be performed at the first asynchronous opportunity. As funções resolve e reject, quand… Promises can be consumed by registering functions using .then and .catch methods.. then() then() is invoked when a promise is either resolved or rejected. Comprehension is enhanced by seeing the errors actually occur. Esta função é executada imediatamente pela implementação do Promise, passando as funções resolve e reject. Note that promises are guaranteed to be asynchronous. They can fill in their email addresses, so that when the song becomes available, all subscribed parties instantly receive it. To learn about the way promises work and how you can use them, we advise you to read Handling a rejected promise too early has consequences further down the promise chain. O executor é chamado antes que o construtor de Promise retorne o objeto criado. To understand this, start by scrolling to the bottom of the code block, and examine the promise chain. Parameters: then() method takes two functions as parameters. Promise.all takes an array of promises (it technically can be any iterable, but is usually an array) and returns a new promise.. To contribute to this compatibility data, please write a pull request against this repository: onRejected – срабатывают, когда promise в состоянии «выполнен с … executor 1. If the singer has already released their song and then a person signs up on the subscription list, they probably won’t receive that song. We’ll see that in the next chapters. This function should take two functions as parameters. Subscriptions in real life must be done prior to the event.Promises are more flexible. (You need a browser that supports By clicking the button several times in a short amount of time, you'll even see the different promises being fulfilled one after another.Get the latest and greatest from MDN delivered straight to your inbox.The newsletter is offered in English only at the moment. The first promise in the chain is most deeply nested and is the first to pop.A promise can participate in more than one nesting. Sign in to enjoy the benefits of an MDN account. Sometimes there is no choice, because an error must be handled immediately.

The first of these functions (resolve) is called when the asynchronous task completes successfully and returns the results of the task as a value. Promises Callbacks; Promises allow us to do things in the natural order. You give your fans a list. For instance, the Promise.all below settles after 3 seconds, and then its result is an array [1, 2, 3]: This feels like a good time to warn you that what jQuery calls a promise is in fact totally different to what everyone else calls a promise. This constructor takes as its argument a function, called the \"executor function\". ECMAscript 6 原生提供了 Promise 对象。 Promise 对象代表了未来将要发生的事件，用来传递异步操作的消息。 Promise 对象有以下两个特点: 1、对象的状态不受外界影响。Promise 对象代表一个异步操作，有三种状态： pending: 初始状态，不是成功或失败状态。 fulfilled: 意味着操作成功完成。


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