map.js
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import Promise from './promise';
import {
default as Enumerator
} from './enumerator';
import {
tryCatch,
TRY_CATCH_ERROR,
REJECTED
} from './-internal';
export class MapEnumerator extends Enumerator {
constructor(Constructor, entries, mapFn, label) {
super(Constructor, entries, true, label, mapFn);
}
_init(Constructor, input, bool, label, mapFn) {
let len = input.length || 0;
this.length = len;
this._remaining = len;
this._result = new Array(len);
this._mapFn = mapFn;
this._enumerate(input);
}
_setResultAt(state, i, value, firstPass) {
if (firstPass) {
let val = tryCatch(this._mapFn)(value, i);
if (val === TRY_CATCH_ERROR) {
this._settledAt(REJECTED, i, val.error, false);
} else {
this._eachEntry(val, i, false);
}
} else {
this._remaining--;
this._result[i] = value;
}
}
}
/**
`map` is similar to JavaScript's native `map` method. `mapFn` is eagerly called
meaning that as soon as any promise resolves its value will be passed to `mapFn`.
`map` returns a promise that will become fulfilled with the result of running
`mapFn` on the values the promises become fulfilled with.
For example:
```javascript
import { map, resolve } from 'rsvp';
let promise1 = resolve(1);
let promise2 = resolve(2);
let promise3 = resolve(3);
let promises = [ promise1, promise2, promise3 ];
let mapFn = function(item){
return item + 1;
};
map(promises, mapFn).then(function(result){
// result is [ 2, 3, 4 ]
});
```
If any of the `promises` given to `map` are rejected, the first promise
that is rejected will be given as an argument to the returned promise's
rejection handler. For example:
```javascript
import { map, reject, resolve } from 'rsvp';
let promise1 = resolve(1);
let promise2 = reject(new Error('2'));
let promise3 = reject(new Error('3'));
let promises = [ promise1, promise2, promise3 ];
let mapFn = function(item){
return item + 1;
};
map(promises, mapFn).then(function(array){
// Code here never runs because there are rejected promises!
}, function(reason) {
// reason.message === '2'
});
```
`map` will also wait if a promise is returned from `mapFn`. For example,
say you want to get all comments from a set of blog posts, but you need
the blog posts first because they contain a url to those comments.
```javscript
import { map } from 'rsvp';
let mapFn = function(blogPost){
// getComments does some ajax and returns an Promise that is fulfilled
// with some comments data
return getComments(blogPost.comments_url);
};
// getBlogPosts does some ajax and returns an Promise that is fulfilled
// with some blog post data
map(getBlogPosts(), mapFn).then(function(comments){
// comments is the result of asking the server for the comments
// of all blog posts returned from getBlogPosts()
});
```
@method map
@public
@static
@for rsvp
@param {Array} promises
@param {Function} mapFn function to be called on each fulfilled promise.
@param {String} label optional string for labeling the promise.
Useful for tooling.
@return {Promise} promise that is fulfilled with the result of calling
`mapFn` on each fulfilled promise or value when they become fulfilled.
The promise will be rejected if any of the given `promises` become rejected.
*/
export default function map(promises, mapFn, label) {
if (typeof mapFn !== 'function') {
return Promise.reject(new TypeError("map expects a function as a second argument"), label);
}
return Promise.resolve(promises, label)
.then(function(promises) {
if (!Array.isArray(promises)) {
throw new TypeError("map must be called with an array");
}
return new MapEnumerator(Promise, promises, mapFn, label).promise;
});
}