npm package: @stdlib/utils-do-while
Description: Invoke a function while a test condition is true.
Author: The Stdlib Authors
Latest version: 0.2.3

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# doWhile

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-url] -->

> Invoke a function while a test condition is true.

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<section class="intro">

</section>

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<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/utils-do-while
```

</section>

<section class="usage">

## Usage

```javascript
var doWhile = require( '@stdlib/utils-do-while' );
```

#### doWhile( fcn, predicate\[, thisArg ] )

Invokes a `function` until a `predicate` function returns `false`. Note that the `predicate` function is evaluated **after** executing `fcn`; thus, `fcn` **always** executes at least once.

```javascript
function predicate( i ) {
    return ( i < 5 );
}

function beep( i ) {
    console.log( 'boop: %d', i );
}

doWhile( beep, predicate );
/* =>
    boop: 0
    boop: 1
    boop: 2
    boop: 3
    boop: 4
*/
```

Both the `predicate` function and the `function` to invoke are provided a single argument:

-   **i**: iteration number (starting from zero).

To set the function execution context for the invoked function, provide a `thisArg`.

```javascript
function predicate( i ) {
    return ( i < 5 );
}

function count() {
    this.count += 1;
}

var context = {
    'count': 0
};

doWhile( count, predicate, context );

console.log( context.count );
// => 5
```

</section>

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<section class="notes">

</section>

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<!-- Package usage examples. -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
var randu = require( '@stdlib/random-base-randu' );
var doWhile = require( '@stdlib/utils-do-while' );

function predicate() {
    return ( randu() > 0.05 );
}

function log( i ) {
    console.log( i );
}

doWhile( log, predicate );
```

</section>

<!-- /.examples -->

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* * *

## See Also

-   <span class="package-name">[`@stdlib/utils-do-until`][@stdlib/utils/do-until]</span><span class="delimiter">: </span><span class="description">invoke a function until a test condition is true.</span>
-   <span class="package-name">[`@stdlib/utils-async/do-while`][@stdlib/utils/async/do-while]</span><span class="delimiter">: </span><span class="description">invoke a function while a test condition is true.</span>
-   <span class="package-name">[`@stdlib/utils-do-while-each`][@stdlib/utils/do-while-each]</span><span class="delimiter">: </span><span class="description">while a test condition is true, invoke a function for each element in a collection.</span>
-   <span class="package-name">[`@stdlib/utils-until`][@stdlib/utils/until]</span><span class="delimiter">: </span><span class="description">invoke a function until a test condition is true.</span>
-   <span class="package-name">[`@stdlib/utils-while`][@stdlib/utils/while]</span><span class="delimiter">: </span><span class="description">invoke a function while a test condition is true.</span>

</section>

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<section class="main-repo" >

* * *

## 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 &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

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[@stdlib/utils/do-until]: https://www.npmjs.com/package/@stdlib/utils-do-until

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