utils-async-map-keys

Map keys from one object to a new object having the same values.

https://github.com/stdlib-js/utils-async-map-keys

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Keywords

async asynchronous clone copy cp create extract javascript keys map node node-js nodejs property stdlib transform util utilities utility utils

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iterator assert

Last synced: 6 months ago · JSON representation ·

Repository

Map keys from one object to a new object having the same values.

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Host: GitHub
Owner: stdlib-js
License: apache-2.0
Language: JavaScript
Default Branch: main
Homepage: https://github.com/stdlib-js/stdlib
Size: 1.14 MB

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Topics

async asynchronous clone copy cp create extract javascript keys map node node-js nodejs property stdlib transform util utilities utility utils

Created over 4 years ago · Last pushed 8 months ago

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Readme Changelog Contributing License Code of conduct Citation Security

We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.

The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.

When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.

To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!

mapKeysAsync

Map keys from one object to a new object having the same values.

## Installation ```bash npm install @stdlib/utils-async-map-keys ``` Alternatively, - To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]). - If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions). - For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]). The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships. To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

## Usage ```javascript var mapKeysAsync = require( '@stdlib/utils-async-map-keys' ); ``` #### mapKeysAsync( obj, \[options,] transform, done ) Map keys from one `object` to a new `object` having the same values. ```javascript function transform( key, next ) { setTimeout( onTimeout, 0 ); function onTimeout() { next( null, key+':beep' ); } } function done( error, out ) { if ( error ) { throw error; } console.log( out ); // => { 'a:beep': 1, 'b:beep': 2 } } var obj = { 'a': 1, 'b': 2 }; mapKeysAsync( obj, transform, done ); ``` The `next` callback accepts two arguments: `error` and `key`. The second argument to the `next` callback is the transformed property name. If a `transform` function calls the `next` callback with a truthy error argument, the function stops processing any additional own properties and calls the `done` callback for error processing. ```javascript function transform( key, value, next ) { setTimeout( onTimeout, value ); function onTimeout() { if ( value === 1 ) { return next( new Error( 'boop' ) ); } next( null, key+':beep' ); } } function done( error ) { if ( error ) { console.error( error.message ); // => 'boop' } } var obj = { 'a': 1, 'b': 2 }; mapKeysAsync( obj, transform, done ); ``` The function accepts the following `options`: - `limit`: the maximum number of pending invocations at any one time. Default: `infinity`. - `series`: `boolean` indicating whether to sequentially invoke the `transform` function for each own property. If `true`, the function sets `options.limit=1`. Default: `false`. - `thisArg`: the execution context for `fcn`. By default, all properties are processed concurrently, which means that the function does **not** guarantee completion order. To process each property sequentially, set the `series` option to `true`. ```javascript function transform( key, value, next ) { setTimeout( onTimeout, value ); function onTimeout() { next( null, key+':beep' ); } } function done( error, out ) { if ( error ) { throw error; } console.log( out ); // => { 'a:beep': 1, 'b:beep': 2 } } var obj = { 'a': 1, 'b': 2 }; var opts = { 'series': true }; mapKeysAsync( obj, opts, transform, done ); ``` To limit the maximum number of pending function invocations, set the `limit` option. ```javascript function transform( key, value, next ) { setTimeout( onTimeout, value ); function onTimeout() { next( null, key+':beep' ); } } function done( error, out ) { if ( error ) { throw error; } console.log( out ); // => { 'a:beep': 1, 'b:beep': 2, 'c:beep': 3 } } var obj = { 'a': 1, 'b': 2, 'c': 3 }; var opts = { 'limit': 2 }; mapKeysAsync( obj, opts, transform, done ); ``` To set the execution context of the `transform` function, set the `thisArg` option. ```javascript function transform( key, value, next ) { this.count += 1; setTimeout( onTimeout, value ); function onTimeout() { next( null, key+':beep' ); } } var obj = { 'a': 1, 'b': 2, 'c': 3 }; var context = { 'count': 0 }; var opts = { 'thisArg': context }; mapKeysAsync( obj, opts, transform, done ); function done( error, out ) { if ( error ) { throw error; } console.log( out ); // => { 'a:beep': 1, 'b:beep': 2, 'c:beep': 3 } console.log( context.count ); // => 3 } ``` When invoked, the `transform` function is provided a maximum of four arguments: - `key`: object key. - `value`: object value corresponding to `key`. - `obj`: source object. - `next`: a callback which should be called once the `transform` function has finished processing a property. The actual number of provided arguments depends on function `length`. If the `transform` function accepts two arguments, the `transform` function is provided `key` and `next`. If the `transform` function accepts three arguments, the `transform` function is provided `key`, `value`, and `next`. For every other `transform` function signature, the `transform` function is provided all four arguments. ```javascript function transform( key, value, obj, next ) { console.log( 'obj: %s. %s: %d', JSON.stringify( obj ), key, value ); setTimeout( onTimeout, value ); function onTimeout() { next( null, key+':'+value ); } } function done( error, out ) { if ( error ) { throw error; } console.log( out ); } var obj = { 'a': 1, 'b': 2 }; mapKeysAsync( obj, transform, done ); /* => e.g., obj: {"a": 1, "b": 2}. a: 1 obj: {"a": 1, "b": 2}. b: 2 { 'a:1': 1, 'b:2': 2 } */ ``` #### mapKeysAsync.factory( \[options,] transform ) Returns a `function` which invokes a `transform` function once for each own property. ```javascript function transform( key, value, next ) { setTimeout( onTimeout, value ); function onTimeout() { next( null, key+':beep' ); } } function done( error, out ) { if ( error ) { throw error; } console.log( out ); } var f = mapKeysAsync.factory( transform ); var obj1 = { 'a': 1, 'b': 2 }; f( obj1, done ); // => { 'a:beep': 1, 'b:beep': 2 } var obj2 = { 'c': 3, 'd': 4 }; f( obj2, done ); // => { 'c:beep': 3, 'd:beep': 4 } ``` The function accepts the same `options` as `mapKeysAsync()`.

## Notes - If a provided function calls the `next` callback with a truthy `error` argument, the function suspends execution and immediately calls the `done` callback for subsequent `error` handling. - If provided an empty `object`, the function calls the `done` callback with an empty `object`. - Key iteration order is **not** guaranteed, as `object` key enumeration is not specified according to the [ECMAScript specification][ecma-262]. In practice, however, most engines use insertion order to sort an `object`'s keys, thus allowing for iteration order. - Key insertion order is **not** guaranteed. - The value returned by a `transform` function should be a value which can be serialized as an `object` key. - The function only maps **own** properties. Hence, the function does **not** map inherited properties. - The function **shallow** copies key values. - **Neither** `mapKeysAsync` nor the function returned by the `factory` method **guarantee** asynchronous execution. To guarantee asynchrony, wrap the `done` callback in a function which either executes at the end of the current stack (e.g., `nextTick`) or during a subsequent turn of the event loop (e.g., `setImmediate`, `setTimeout`).

## Examples ```javascript var resolve = require( 'path' ).resolve; var readFile = require( '@stdlib/fs-read-file' ); var mapKeysAsync = require( '@stdlib/utils-async-map-keys' ); var files = { 'file1': resolve( __dirname, 'package.json' ), 'file2': resolve( __dirname, 'README.md' ) }; function read( key, value, next ) { var opts = { 'encoding': 'utf8' }; readFile( value, opts, onFile ); function onFile( error ) { if ( error ) { return next( error, key+':unreadable' ); } next( null, key+':readable' ); } } function done( error, out ) { if ( error ) { throw error; } console.log( out ); } mapKeysAsync( files, read, done ); ```

* * * ## Notice This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more. For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib]. #### Community [![Chat][chat-image]][chat-url] --- ## License See [LICENSE][stdlib-license]. ## Copyright Copyright © 2016-2025. The Stdlib [Authors][stdlib-authors].

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Standard library for JavaScript.

Citation (CITATION.cff)

cff-version: 1.2.0
title: stdlib
message: >-
  If you use this software, please cite it using the
  metadata from this file.

type: software

authors:
  - name: The Stdlib Authors
    url: https://github.com/stdlib-js/stdlib/graphs/contributors

repository-code: https://github.com/stdlib-js/stdlib
url: https://stdlib.io

abstract: |
  Standard library for JavaScript and Node.js.

keywords:
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  - standard library
  - scientific computing
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  - statistical computing

license: Apache-2.0 AND BSL-1.0

date-released: 2016

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npmjs.org: @stdlib/utils-async-map-keys

Map keys from one object to a new object having the same values.

Homepage: https://stdlib.io
License: Apache-2.0
Latest release: 0.2.2
published over 1 year ago

Versions: 12
Dependent Packages: 3
Dependent Repositories: 1
Downloads: 9 Last month

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Forks count: 15.4%

Downloads: 25.6%

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@stdlib/bench ^0.0.x development
@stdlib/fs-read-file ^0.0.x development
@stdlib/random-base-randu ^0.0.x development
@stdlib/utils-noop ^0.0.x development
istanbul ^0.4.1 development
tap-spec 5.x.x development
tape git+https://github.com/kgryte/tape.git#fix/globby development
@stdlib/assert-has-own-property ^0.0.x
@stdlib/assert-is-boolean ^0.0.x
@stdlib/assert-is-function ^0.0.x
@stdlib/assert-is-plain-object ^0.0.x
@stdlib/assert-is-positive-integer ^0.0.x
@stdlib/constants-float64-pinf ^0.0.x
@stdlib/string-format ^0.0.x
@stdlib/utils-define-nonenumerable-read-only-property ^0.0.x
@stdlib/utils-keys ^0.0.x
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