Function

map (promises, mapFn, label) Promise public

Module: rsvp

Defined in node_modules/rsvp/lib/rsvp/map.js:39

promises
Array
mapFn
Function
function to be called on each fulfilled promise.
label
String
optional string for labeling the promise. Useful for tooling.
returns
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.

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:

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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:

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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.

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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()
});