# now-and-later [![NPM version][npm-image]][npm-url] [![Downloads][downloads-image]][npm-url] [![Build Status][travis-image]][travis-url] [![AppVeyor Build Status][appveyor-image]][appveyor-url] [![Coveralls Status][coveralls-image]][coveralls-url] [![Gitter chat][gitter-image]][gitter-url] Map over an array or object of values in parallel or series, passing each through the async iterator, with optional lifecycle hooks. ## Usage ```js var nal = require('now-and-later'); function iterator(value, key, cb){ // called with each value in sequence // also passes the key cb(null, value * 2) } function create(value, key){ // called at the beginning of every iteration // return a storage object to be passed to each lifecycle method return { key: key, value: value }; } function before(storage){ // called before the iterator function of every iteration // receives the storage returned from `create` } function after(result, storage){ // called after a success occurs in the iterator function of any iteration // receives the `result` of the iterator and the storage returned from `create` } function error(error, storage){ // called after an error occurs in the iterator function of any iteration // receives the `error` of the iterator and the storage returned from `create` } function done(error, results) { // called after all iterations complete or an error occurs in an iterator // receives an `error` if one occurred and all results (or partial results upon error) of the iterators } /* Calling mapSeries with an object can't guarantee order It uses Object.keys to get an order It is better to use an array if order must be guaranteed */ nal.mapSeries([1, 2, 3], iterator, { create: create, before: before, after: after, error: error }, done); nal.map({ iter1: 1, iter2: 2 }, iterator, { create: create, before: before, after: after, error: error }, done); ``` ## API ### `map(values, iterator[, extensions][, callback])` Takes an object or array of `values` and an `iterator` function to execute with each value. Optionally, takes an `extensions` object and a `callback` function that is called upon completion of the iterations. All iterations run in parallel. #### `values` An array or object of values to iterate over. If `values` is an array, iterations are started in order by index. If `values` is an object, iterations are started in order by the order returned by `Object.keys` (order is not guaranteed). If `values` is an array, the results of each iteration will be mapped to an array. If `values` is an object, the results of each iteration will be mapped to an object with corresponding keys. #### `iterator(value, key, done)` An async function called per iteration. All iterations are run in parallel. The `iterator` function is called once with each `value`, `key` and a function (`done(error, result)`) to call when the async work is complete. If `done` is passed an error as the first argument, the iteration will fail and the sequence will be ended; however, any iterations in progress will still complete. If `done` is passed a `result` value as the second argument, it will be added to the final results array or object. #### `extensions` The `extensions` object is used for specifying functions that give insight into the lifecycle of each iteration. The possible extension points are `create`, `before`, `after` and `error`. If an extension point is not specified, it defaults to a no-op function. ##### `extensions.create(value, key)` Called at the very beginning of each iteration with the `value` being iterated and the `key` from the array or object. If `create` returns a value (`storage`), it is passed to the `before`, `after` and `error` extension points. If a value is not returned, an empty object is used as `storage` for each other extension point. This is useful for tracking information across an iteration. ##### `extensions.before(storage)` Called immediately before each iteration with the `storage` value returned from the `create` extension point. ##### `extensions.after(result, storage)` Called immediately after each iteration with the `result` of the iteration and the `storage` value returned from the `create` extension point. ##### `extensions.error(error, storage)` Called immediately after a failed iteration with the `error` of the iteration and the `storage` value returned from the `create` extension point. #### `callback(error, results)` A function that is called after all iterations have completed or one iteration has errored. If all iterations completed successfully, the `error` argument will be empty and the `results` will be a mapping of the `iterator` results. If an iteration errored, the `error` argument will be passed from that iteration and the `results` will be whatever partial results had completed successfully before the error occurred. ### `mapSeries(values, iterator[, extensions][, callback])` Takes an object or array of `values` and an `iterator` function to execute with each value. Optionally, takes an `extensions` object and a `callback` function that is called upon completion of the iterations. All iterations run in serial. #### `values` An array or object of values to iterate over. If `values` is an array, iterations are started in order by index. If `values` is an object, iterations are started in order by the order returned by `Object.keys` (order is not guaranteed). If `values` is an array, the results of each iteration will be mapped to an array. If `values` is an object, the results of each iteration will be mapped to an object with corresponding keys. #### `iterator(value, key, done)` An async function called per iteration. All iterations are run in serial. The `iterator` function is called once with each `value`, `key` and a function (`done(error, result)`) to call when the async work is complete. If `done` is passed an error as the first argument, the iteration will fail and the sequence will be ended without executing any more iterations. If `done` is passed a `result` value as the second argument, it will be added to the final results array or object. #### `extensions` The `extensions` object is used for specifying functions that give insight into the lifecycle of each iteration. The possible extension points are `create`, `before`, `after` and `error`. If an extension point is not specified, it defaults to a no-op function. ##### `extensions.create(value, key)` Called at the very beginning of each iteration with the `value` being iterated and the `key` from the array or object. If `create` returns a value (`storage`), it is passed to the `before`, `after` and `error` extension points. If a value is not returned, an empty object is used as `storage` for each other extension point. This is useful for tracking information across an iteration. ##### `extensions.before(storage)` Called immediately before each iteration with the `storage` value returned from the `create` extension point. ##### `extensions.after(result, storage)` Called immediately after each iteration with the `result` of the iteration and the `storage` value returned from the `create` extension point. ##### `extensions.error(error, storage)` Called immediately after a failed iteration with the `error` of the iteration and the `storage` value returned from the `create` extension point. #### `callback(error, results)` A function that is called after all iterations have completed or one iteration has errored. If all iterations completed successfully, the `error` argument will be empty and the `results` will be a mapping of the `iterator` results. If an iteration errored, the `error` argument will be passed from that iteration and the `results` will be whatever partial results had completed successfully before the error occurred. ## License MIT [downloads-image]: http://img.shields.io/npm/dm/now-and-later.svg [npm-url]: https://www.npmjs.com/package/now-and-later [npm-image]: http://img.shields.io/npm/v/now-and-later.svg [travis-url]: https://travis-ci.org/gulpjs/now-and-later [travis-image]: http://img.shields.io/travis/gulpjs/now-and-later.svg?label=travis-ci [appveyor-url]: https://ci.appveyor.com/project/gulpjs/now-and-later [appveyor-image]: https://img.shields.io/appveyor/ci/gulpjs/now-and-later.svg?label=appveyor [coveralls-url]: https://coveralls.io/r/gulpjs/now-and-later [coveralls-image]: http://img.shields.io/coveralls/gulpjs/now-and-later/master.svg [gitter-url]: https://gitter.im/gulpjs/gulp [gitter-image]: https://badges.gitter.im/gulpjs/gulp.svg