На promise можно навешивать колбэки двух типов: onFulfilled – срабатывают, когда promise в состоянии «выполнен успешно». You give your fans a list. 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. Esta função é executada imediatamente pela implementação do Promise, passando as funções resolve e reject. Sign in to enjoy the benefits of an MDN account. The chain is composed of This code can be run under NodeJS. O executor é chamado antes que o construtor de Promise retorne o objeto criado. If you haven’t already created an account, you will be prompted to do so after signing in. Upon provision of an initial promise, a chain of promises can follow. : We can call .then on a Promise as many times as we want. Any termination other than a The promises of a chain are nested like Russian dolls, but get popped like the top of a stack. Promises can be consumed by registering functions using .then and .catch methods.. then() then() is invoked when a promise is either resolved or rejected. p Promises are useful both in node.js and the browser. Parameters: then() method takes two functions as parameters. In that case the action (if appropriate) will be performed at the first asynchronous opportunity. 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. As funções resolve e reject, quand…

A Promise object is created using the new keyword and its constructor. executor 1. (See The signatures of these two functions are simple, they accept a single parameter of any type. When it is finished with the attempt it calls Later we’ll see how “fans” can subscribe to these changes.Here’s an example of a promise constructor and a simple executor function with “producing code” that takes time (via The executor is called automatically and immediately (by After one second of “processing” the executor calls That was an example of a successful job completion, a “fulfilled promise”.And now an example of the executor rejecting the promise with an error:To summarize, the executor should perform a job (usually something that takes time) and then call A promise that is either resolved or rejected is called “settled”, as opposed to an initially “pending” promise.The idea is that a job done by the executor may have only one result or an error.In case something goes wrong, the executor should call In practice, an executor usually does something asynchronously and calls For instance, this might happen when we start to do a job but then see that everything has already been completed and cached.That’s fine. (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. To contribute to this compatibility data, please write a pull request against this repository: The first of these functions (resolve) is called when the asynchronous task completes successfully and returns the results of the task as a value. They can fill in their email addresses, so that when the song becomes available, all subscribed parties instantly receive it. To understand this, start by scrolling to the bottom of the code block, and examine the promise chain. Therefore, an action for an already "settled" promise will occur only after the stack has cleared and a clock-tick has passed. And even if something goes very wrong, say, a fire in the studio, so that you can’t publish the song, they will still be notified.Everyone is happy: you, because the people don’t crowd you anymore, and fans, because they won’t miss the single.This is a real-life analogy for things we often have in programming:The analogy isn’t terribly accurate, because JavaScript promises are more complex than a simple subscription list: they have additional features and limitations. 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. Although, as I mentioned, jQuery's Deferreds are a bit … unhelpful. But it’s fine to begin with.When the executor obtains the result, be it soon or late, doesn’t matter, it should call one of these callbacks:So to summarize: the executor runs automatically and attempts to perform a job. The effect is much like that of This example shows diverse techniques for using Promise capabilities, and diverse situations that can occur. This constructor takes as its argument a function, called the \"executor function\". This function should take two functions as parameters. The termination condition of these functions determines the "settled" state of the next promise in the chain. Note that promises are guaranteed to be asynchronous. For instance, the Promise.all below settles after 3 seconds, and then its result is an array [1, 2, 3]:

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