import Promise from './promise'; import {
isFunction
} from './utils';
/**
`RSVP.filter` is similar to JavaScript's native `filter` method, except that it waits for all promises to become fulfilled before running the `filterFn` on each item in given to `promises`. `RSVP.filter` returns a promise that will become fulfilled with the result of running `filterFn` on the values the promises become fulfilled with. For example: ```javascript var promise1 = RSVP.resolve(1); var promise2 = RSVP.resolve(2); var promise3 = RSVP.resolve(3); var promises = [promise1, promise2, promise3]; var filterFn = function(item){ return item > 1; }; RSVP.filter(promises, filterFn).then(function(result){ // result is [ 2, 3 ] }); ``` If any of the `promises` given to `RSVP.filter` are rejected, the first promise that is rejected will be given as an argument to the returned promise's rejection handler. For example: ```javascript var promise1 = RSVP.resolve(1); var promise2 = RSVP.reject(new Error('2')); var promise3 = RSVP.reject(new Error('3')); var promises = [ promise1, promise2, promise3 ]; var filterFn = function(item){ return item > 1; }; RSVP.filter(promises, filterFn).then(function(array){ // Code here never runs because there are rejected promises! }, function(reason) { // reason.message === '2' }); ``` `RSVP.filter` will also wait for any promises returned from `filterFn`. For instance, you may want to fetch a list of users then return a subset of those users based on some asynchronous operation: ```javascript var alice = { name: 'alice' }; var bob = { name: 'bob' }; var users = [ alice, bob ]; var promises = users.map(function(user){ return RSVP.resolve(user); }); var filterFn = function(user){ // Here, Alice has permissions to create a blog post, but Bob does not. return getPrivilegesForUser(user).then(function(privs){ return privs.can_create_blog_post === true; }); }; RSVP.filter(promises, filterFn).then(function(users){ // true, because the server told us only Alice can create a blog post. users.length === 1; // false, because Alice is the only user present in `users` users[0] === bob; }); ``` @method filter @static @for RSVP @param {Array} promises @param {Function} filterFn - function to be called on each resolved value to filter the final results. @param {String} label optional string describing the promise. Useful for tooling. @return {Promise}
*/ export default function filter(promises, filterFn, label) {
return Promise.all(promises, label).then(function(values) { if (!isFunction(filterFn)) { throw new TypeError("You must pass a function as filter's second argument."); } var length = values.length; var filtered = new Array(length); for (var i = 0; i < length; i++) { filtered[i] = filterFn(values[i]); } return Promise.all(filtered, label).then(function(filtered) { var results = new Array(length); var newLength = 0; for (var i = 0; i < length; i++) { if (filtered[i]) { results[newLength] = values[i]; newLength++; } } results.length = newLength; return results; }); });
}