# now-and-later > Map over an array or object of values in parallel or series, passing each through the async iterator, with optional lifecycle hooks. Latest version **3.0.0** (published 2022-06-25) · MIT license · 0 weekly downloads ## Install ```sh npm install now-and-later pnpm add now-and-later yarn add now-and-later bun add now-and-later ``` ## Health **Score 15/100 (F)** — status: abandoned. Positive: no vulnerabilities. Warnings: low downloads; no types; no esm support. Negative: abandoned; low maintenance score. ## Facts | | | |---|---| | Version | 3.0.0 | | Published | 2022-06-25 | | First published | 2014-08-17 | | Weekly downloads | 0 | | License | MIT | | TypeScript types | none | | Module format | CommonJS | | Node | >= 10.13.0 | | Dependencies | 1 | | Unpacked size | 14.7 KB | | Known vulnerabilities | 0 | | Install scripts | no | | GitHub stars | 24 | | Author | Gulp Team | | Maintainers | yocontra, phated | | Keywords | async, parallel, series, each, async.js, map, control, flow, extension, tracing, debug, aop, aspect, timing, tracing | ## Links - npm: https://www.npmjs.com/package/now-and-later - Repository: https://github.com/gulpjs/now-and-later - Homepage: https://github.com/gulpjs/now-and-later#readme - Issues: https://github.com/gulpjs/now-and-later/issues - npm.io page: https://npm.io/package/now-and-later ## Dependencies (1) - [once](https://npm.io/package/once.md) ^1.4.0 ## Alternatives - [@commercetools/sync-actions](https://npm.io/package/@commercetools/sync-actions.md) — 25.1K weekly downloads - [cwait](https://npm.io/package/cwait.md) — 21.4K weekly downloads - [@ledgerhq/hw-app-cosmos](https://npm.io/package/@ledgerhq/hw-app-cosmos.md) — 4.2K weekly downloads - [@financial-times/o-loading](https://npm.io/package/@financial-times/o-loading.md) — 2.8K weekly downloads - [fa](https://npm.io/package/fa.md) — 185 weekly downloads ## Recent versions - 3.0.0 (latest) — 2022-06-25 - 2.0.1 — 2019-04-06 - 2.0.0 — 2017-06-17 - 1.0.0 — 2016-06-27 - 0.0.6 — 2014-09-01 - 0.0.5 — 2014-08-31 - 0.0.4 — 2014-08-23 - 0.0.3 — 2014-08-18 - 0.0.2 — 2014-08-17 - 0.0.1 — 2014-08-17 - 0.0.0 — 2014-08-17 ## README

# now-and-later [![NPM version][npm-image]][npm-url] [![Downloads][downloads-image]][npm-url] [![Build Status][ci-image]][ci-url] [![Coveralls Status][coveralls-image]][coveralls-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[, options][, callback])` Takes an object or array of `values` and an `iterator` function to execute with each value. Optionally, takes an `options` 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. #### `options` The `options` object is primarily 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. The `options` object for `map` also allows specifying `concurrency` in which to run your iterations. By default, your iterations will run at maximum concurrency. ##### `options.concurrency` Limits the amount of iterations allowed to run at a given time. ##### `options.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. ##### `options.before(storage)` Called immediately before each iteration with the `storage` value returned from the `create` extension point. ##### `options.after(result, storage)` Called immediately after each iteration with the `result` of the iteration and the `storage` value returned from the `create` extension point. ##### `options.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[, options][, callback])` Takes an object or array of `values` and an `iterator` function to execute with each value. Optionally, takes an `options` 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. #### `options` The `options` object is primarily 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. ##### `options.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. ##### `options.before(storage)` Called immediately before each iteration with the `storage` value returned from the `create` extension point. ##### `options.after(result, storage)` Called immediately after each iteration with the `result` of the iteration and the `storage` value returned from the `create` extension point. ##### `options.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]: https://img.shields.io/npm/dm/now-and-later.svg?style=flat-square [npm-url]: https://www.npmjs.com/package/now-and-later [npm-image]: https://img.shields.io/npm/v/now-and-later.svg?style=flat-square [ci-url]: https://github.com/gulpjs/now-and-later/actions?query=workflow:dev [ci-image]: https://img.shields.io/github/workflow/status/gulpjs/now-and-later/dev?style=flat-square [coveralls-url]: https://coveralls.io/r/gulpjs/now-and-later [coveralls-image]: https://img.shields.io/coveralls/gulpjs/now-and-later/master.svg?style=flat-square --- _Source: https://npm.io/package/now-and-later · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._