Make minor grammar corrections/updates to async/promise-basics

This commit is contained in:
Jonathan Chue 2019-12-07 16:40:31 -08:00
parent 5b195795da
commit 4c650b54b7

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@ -22,7 +22,7 @@ let promise = new Promise(function(resolve, reject) {
}); });
``` ```
The function passed to `new Promise` is called the *executor*. When `new Promise` is created, it runs automatically. It contains the producing code, that should eventually produce a result. In terms of the analogy above: the executor is the "singer". The function passed to `new Promise` is called the *executor*. When `new Promise` is created, it runs automatically. It contains the producing code, that should eventually produce a result. In terms of the analogy above, the executor is the "singer".
Its arguments `resolve` and `reject` are callbacks provided by JavaScript itself. Our code is only inside the executor. Its arguments `resolve` and `reject` are callbacks provided by JavaScript itself. Our code is only inside the executor.
@ -31,9 +31,9 @@ When the executor obtains the result, be it soon or late - doesn't matter, it sh
- `resolve(value)` — if the job finished successfully, with result `value`. - `resolve(value)` — if the job finished successfully, with result `value`.
- `reject(error)` — if an error occurred, `error` is the error object. - `reject(error)` — if an error occurred, `error` is the error object.
So to summarize: the executor runs automatically, it should do a job and then call either `resolve` or `reject`. So to summarize: the executor runs automatically. It performs a job and then calls either `resolve` or `reject`.
The `promise` object returned by `new Promise` constructor has internal properties: The `promise` object returned by the `new Promise` constructor has internal properties:
- `state` — initially `"pending"`, then changes to either `"fulfilled"` when `resolve` is called or `"rejected"` when `reject` is called. - `state` — initially `"pending"`, then changes to either `"fulfilled"` when `resolve` is called or `"rejected"` when `reject` is called.
- `result` — initially `undefined`, then changes to `value` when `resolve(value)` called or `error` when `reject(error)` is called. - `result` — initially `undefined`, then changes to `value` when `resolve(value)` called or `error` when `reject(error)` is called.
@ -58,7 +58,7 @@ let promise = new Promise(function(resolve, reject) {
We can see two things by running the code above: 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 should only 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 should only call one of them when ready.
After one second of "processing" the executor calls `resolve("done")` to produce the result. This changes the state of the `promise` object: After one second of "processing" the executor calls `resolve("done")` to produce the result. This changes the state of the `promise` object:
@ -79,7 +79,7 @@ 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 perform a job (usually something that takes time) and then call `resolve` or `reject` to change the state of the corresponding promise object.
A promise that is either resolved or rejected is called "settled", as opposed to an initially "pending" promise. A promise that is either resolved or rejected is called "settled", as opposed to an initially "pending" promise.
@ -166,7 +166,7 @@ promise.then(
The first function was executed. The first function was executed.
And in the case of a rejection -- the second one: And in the case of a rejection, the second one:
```js run ```js run
let promise = new Promise(function(resolve, reject) { let promise = new Promise(function(resolve, reject) {
@ -205,7 +205,7 @@ let promise = new Promise((resolve, reject) => {
}); });
*!* *!*
// .catch(f) is the same as .then(null, f) // .catch(f) is the same as promise.then(null, f)
promise.catch(alert); // shows "Error: Whoops!" after 1 second promise.catch(alert); // shows "Error: Whoops!" after 1 second
*/!* */!*
``` ```