216 lines
8.6 KiB
Markdown
216 lines
8.6 KiB
Markdown
<p align="center">
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<a href="https://gulpjs.com">
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<img height="257" width="114" src="https://raw.githubusercontent.com/gulpjs/artwork/master/gulp-2x.png">
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</a>
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</p>
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# now-and-later
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[![NPM version][npm-image]][npm-url] [![Downloads][downloads-image]][npm-url] [![Build Status][ci-image]][ci-url] [![Coveralls Status][coveralls-image]][coveralls-url]
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Map over an array or object of values in parallel or series, passing each through the async iterator, with optional lifecycle hooks.
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## Usage
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```js
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var nal = require('now-and-later');
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function iterator(value, key, cb) {
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// called with each value in sequence
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// also passes the key
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cb(null, value * 2);
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}
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function create(value, key) {
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// called at the beginning of every iteration
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// return a storage object to be passed to each lifecycle method
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return { key: key, value: value };
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}
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function before(storage) {
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// called before the iterator function of every iteration
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// receives the storage returned from `create`
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}
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function after(result, storage) {
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// called after a success occurs in the iterator function of any iteration
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// receives the `result` of the iterator and the storage returned from `create`
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}
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function error(error, storage) {
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// called after an error occurs in the iterator function of any iteration
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// receives the `error` of the iterator and the storage returned from `create`
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}
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function done(error, results) {
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// called after all iterations complete or an error occurs in an iterator
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// receives an `error` if one occurred and all results (or partial results upon error) of the iterators
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}
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/*
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Calling mapSeries with an object can't guarantee order
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It uses Object.keys to get an order
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It is better to use an array if order must be guaranteed
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*/
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nal.mapSeries(
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[1, 2, 3],
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iterator,
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{
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create: create,
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before: before,
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after: after,
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error: error,
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},
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done
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);
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nal.map(
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{
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iter1: 1,
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iter2: 2,
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},
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iterator,
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{
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create: create,
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before: before,
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after: after,
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error: error,
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},
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done
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);
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```
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## API
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### `map(values, iterator[, options][, callback])`
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Takes an object or array of `values` and an `iterator` function to execute with each value.
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Optionally, takes an `options` object and a `callback` function that is called upon completion of the iterations.
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All iterations run in parallel.
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#### `values`
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An array or object of values to iterate over.
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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).
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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.
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#### `iterator(value, key, done)`
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An async function called per iteration. All iterations are run in parallel.
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The `iterator` function is called once with each `value`, `key` and a function (`done(error, result)`) to call when the async work is complete.
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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.
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#### `options`
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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.
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The `options` object for `map` also allows specifying `concurrency` in which to run your iterations. By default, your iterations will run at maximum concurrency.
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##### `options.concurrency`
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Limits the amount of iterations allowed to run at a given time.
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##### `options.create(value, key)`
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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.
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If a value is not returned, an empty object is used as `storage` for each other extension point.
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This is useful for tracking information across an iteration.
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##### `options.before(storage)`
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Called immediately before each iteration with the `storage` value returned from the `create` extension point.
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##### `options.after(result, storage)`
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Called immediately after each iteration with the `result` of the iteration and the `storage` value returned from the `create` extension point.
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##### `options.error(error, storage)`
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Called immediately after a failed iteration with the `error` of the iteration and the `storage` value returned from the `create` extension point.
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#### `callback(error, results)`
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A function that is called after all iterations have completed or one iteration has errored.
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If all iterations completed successfully, the `error` argument will be empty and the `results` will be a mapping of the `iterator` results.
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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.
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### `mapSeries(values, iterator[, options][, callback])`
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Takes an object or array of `values` and an `iterator` function to execute with each value.
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Optionally, takes an `options` object and a `callback` function that is called upon completion of the iterations.
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All iterations run in serial.
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#### `values`
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An array or object of values to iterate over.
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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).
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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.
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#### `iterator(value, key, done)`
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An async function called per iteration. All iterations are run in serial.
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The `iterator` function is called once with each `value`, `key` and a function (`done(error, result)`) to call when the async work is complete.
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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.
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#### `options`
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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.
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##### `options.create(value, key)`
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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.
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If a value is not returned, an empty object is used as `storage` for each other extension point.
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This is useful for tracking information across an iteration.
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##### `options.before(storage)`
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Called immediately before each iteration with the `storage` value returned from the `create` extension point.
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##### `options.after(result, storage)`
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Called immediately after each iteration with the `result` of the iteration and the `storage` value returned from the `create` extension point.
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##### `options.error(error, storage)`
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Called immediately after a failed iteration with the `error` of the iteration and the `storage` value returned from the `create` extension point.
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#### `callback(error, results)`
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A function that is called after all iterations have completed or one iteration has errored.
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If all iterations completed successfully, the `error` argument will be empty and the `results` will be a mapping of the `iterator` results.
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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.
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## License
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MIT
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<!-- prettier-ignore-start -->
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[downloads-image]: https://img.shields.io/npm/dm/now-and-later.svg?style=flat-square
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[npm-url]: https://www.npmjs.com/package/now-and-later
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[npm-image]: https://img.shields.io/npm/v/now-and-later.svg?style=flat-square
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[ci-url]: https://github.com/gulpjs/now-and-later/actions?query=workflow:dev
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[ci-image]: https://img.shields.io/github/workflow/status/gulpjs/now-and-later/dev?style=flat-square
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[coveralls-url]: https://coveralls.io/r/gulpjs/now-and-later
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[coveralls-image]: https://img.shields.io/coveralls/gulpjs/now-and-later/master.svg?style=flat-square
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<!-- prettier-ignore-end -->
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