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Ilya Kantor 2019-09-02 21:55:37 +03:00
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1-js/11-async/02-promise-basics/article.md
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@ -60,9 +60,9 @@ We can see two things by running the code above:
1. The executor is called automatically and immediately (by `new Promise`). 1. The executor is called automatically and immediately (by `new Promise`).
2. The executor receives two arguments: `resolve` and `reject` — these functions are pre-defined by the JavaScript engine. So we don't need to create them. We only should call one of them when ready. 2. The executor receives two arguments: `resolve` and `reject` — these functions are pre-defined by the JavaScript engine. So we don't need to create them. We only should call one of them when ready.
After one second of "processing" the executor calls `resolve("done")` to produce the result: After one second of "processing" the executor calls `resolve("done")` to produce the result. This changes the state of the `promise` object:
![](promise-resolve-1.svg) ![](promise-resolve-1.svg)
That was an example of a successful job completion, a "fulfilled promise". That was an example of a successful job completion, a "fulfilled promise".
@ -75,14 +75,16 @@ let promise = new Promise(function(resolve, reject) {
}); });
``` ```
The call to `reject(...)` moves the promise object to `"rejected"` state:
![](promise-reject-1.svg) ![](promise-reject-1.svg)
To summarize, the executor should do a job (something that takes time usually) and then call `resolve` or `reject` to change the state of the corresponding Promise object. To summarize, the executor should do a job (something that takes time usually) and then call `resolve` or `reject` to change the state of the corresponding promise object.
The Promise that is either resolved or rejected is called "settled", as opposed to a initially "pending" Promise. A promise that is either resolved or rejected is called "settled", as opposed to a initially "pending" promise.
````smart header="There can be only a single result or an error" ````smart header="There can be only a single result or an error"
The executor should call only one `resolve` or one `reject`. The promise's state change is final. The executor should call only one `resolve` or one `reject`. Any state change is final.
All further calls of `resolve` and `reject` are ignored: All further calls of `resolve` and `reject` are ignored: