https://github.com/stdlib-js/utils-async-while
Invoke a function while a test condition is true.
https://github.com/stdlib-js/utils-async-while
async asynchronous for iterate iteration javascript loop node node-js nodejs stdlib util utilities utility utils while
Last synced: 29 days ago
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Invoke a function while a test condition is true.
- Host: GitHub
- URL: https://github.com/stdlib-js/utils-async-while
- Owner: stdlib-js
- License: apache-2.0
- Created: 2021-06-13T19:27:08.000Z (almost 5 years ago)
- Default Branch: main
- Last Pushed: 2026-02-23T05:35:54.000Z (about 1 month ago)
- Last Synced: 2026-02-23T09:13:36.923Z (about 1 month ago)
- Topics: async, asynchronous, for, iterate, iteration, javascript, loop, node, node-js, nodejs, stdlib, util, utilities, utility, utils, while
- Language: JavaScript
- Homepage: https://github.com/stdlib-js/stdlib
- Size: 905 KB
- Stars: 2
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- License: LICENSE
- Code of conduct: CODE_OF_CONDUCT.md
- Citation: CITATION.cff
- Security: SECURITY.md
- Notice: NOTICE
Awesome Lists containing this project
README
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# whileAsync
[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url]
> Invoke a function while a test condition is true.
## Installation
```bash
npm install @stdlib/utils-async-while
```
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 whileAsync = require( '@stdlib/utils-async-while' );
```
#### whileAsync( predicate, fcn, done\[, thisArg ] )
Invokes a `function` until a `predicate` function returns `false`.
```javascript
function predicate( i, clbk ) {
clbk( null, i < 5 );
}
function fcn( i, next ) {
setTimeout( onTimeout, 0 );
function onTimeout() {
console.log( 'beep: %d', i );
next();
}
}
function done( error ) {
if ( error ) {
throw error;
}
}
whileAsync( predicate, fcn, done );
/* =>
beep: 0
beep: 1
beep: 2
beep: 3
beep: 4
*/
```
The `predicate` function is provided two arguments:
- `i`: iteration number (starting from zero).
- `clbk`: a callback indicating whether to invoke `fcn`.
The `clbk` function accepts two arguments:
- `error`: error object.
- `bool`: test result.
If the test result is truthy, the function invokes `fcn`; otherwise, the function invokes the `done` callback.
The function to invoke is provided two arguments:
- `i`: iteration number (starting from zero).
- `next`: a callback which must be invoked before proceeding to the next iteration.
The first argument of both `clbk` and `next` is an `error` argument. If either function is called with a truthy `error` argument, the function suspends execution and immediately calls the `done` callback for subsequent `error` handling.
```javascript
function predicate( i, clbk ) {
clbk( null, i < 5 );
}
function fcn( i, next ) {
setTimeout( onTimeout, 0 );
function onTimeout() {
next( new Error( 'beep' ) );
}
}
function done( error ) {
console.error( error.message );
// => beep
}
whileAsync( predicate, fcn, done );
```
The `done` callback is invoked with an `error` argument and any arguments passed to the final `next` callback.
```javascript
function predicate( i, clbk ) {
clbk( null, i < 5 );
}
function fcn( i, next ) {
setTimeout( onTimeout, 0 );
function onTimeout() {
next( null, i );
}
}
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
// => 4
}
whileAsync( predicate, fcn, done );
```
To set the function execution context for the invoked function, provide a `thisArg`.
```javascript
function predicate( i, clbk ) {
clbk( null, i < 5 );
}
function fcn( i, next ) {
this.count += 1;
setTimeout( onTimeout, 0 );
function onTimeout() {
next();
}
}
var context = {
'count': 0
};
whileAsync( predicate, fcn, done, context );
function done( error ) {
if ( error ) {
throw error;
}
console.log( context.count );
// => 5
}
```
## Notes
- Execution is **not** guaranteed to be asynchronous. 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 repeatString = require( '@stdlib/string-repeat' );
var whileAsync = require( '@stdlib/utils-async-while' );
function predicate( i, clbk ) {
setTimeout( onTimeout, 0 );
function onTimeout() {
clbk( null, i < 5 );
}
}
function fcn( i, next ) {
setTimeout( onTimeout, 0 );
function onTimeout() {
next( null, repeatString( 'beep', i+1 ) );
}
}
function done( error, result ) {
if ( error ) {
throw error;
}
console.log( result );
}
whileAsync( predicate, fcn, done );
```
* * *
## See Also
- [`@stdlib/utils-async/do-until`][@stdlib/utils/async/do-until]: invoke a function until a test condition is true.
- [`@stdlib/utils-async/do-while`][@stdlib/utils/async/do-while]: invoke a function while a test condition is true.
- [`@stdlib/utils-async/until`][@stdlib/utils/async/until]: invoke a function until a test condition is true.
- [`@stdlib/utils-while`][@stdlib/utils/while]: invoke a function while a test condition is true.
* * *
## 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].
[npm-image]: http://img.shields.io/npm/v/@stdlib/utils-async-while.svg
[npm-url]: https://npmjs.org/package/@stdlib/utils-async-while
[test-image]: https://github.com/stdlib-js/utils-async-while/actions/workflows/test.yml/badge.svg?branch=main
[test-url]: https://github.com/stdlib-js/utils-async-while/actions/workflows/test.yml?query=branch:main
[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/utils-async-while/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/utils-async-while?branch=main
[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg
[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im
[stdlib]: https://github.com/stdlib-js/stdlib
[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors
[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules
[deno-url]: https://github.com/stdlib-js/utils-async-while/tree/deno
[deno-readme]: https://github.com/stdlib-js/utils-async-while/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/utils-async-while/tree/umd
[umd-readme]: https://github.com/stdlib-js/utils-async-while/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/utils-async-while/tree/esm
[esm-readme]: https://github.com/stdlib-js/utils-async-while/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/utils-async-while/blob/main/branches.md
[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/utils-async-while/main/LICENSE
[@stdlib/utils/async/do-until]: https://github.com/stdlib-js/utils-async-do-until
[@stdlib/utils/async/do-while]: https://github.com/stdlib-js/utils-async-do-while
[@stdlib/utils/async/until]: https://github.com/stdlib-js/utils-async-until
[@stdlib/utils/while]: https://github.com/stdlib-js/utils-while