npm package: @stdlib/utils-async-if-else
Description: If a predicate function returns a truthy value, return `x`; otherwise, return `y`.
Author: The Stdlib Authors
Latest version: 0.2.3

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# ifelseAsync

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

> If a predicate function returns a truthy value, return `x`; otherwise, return `y`.

<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->

<section class="intro">

</section>

<!-- /.intro -->

<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/utils-async-if-else
```

</section>

<section class="usage">

## Usage

```javascript
var ifelseAsync = require( '@stdlib/utils-async-if-else' );
```

#### ifelseAsync( predicate, x, y, done )

If a `predicate` function returns a truthy value, returns `x`; otherwise, returns `y`.

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

function predicate( clbk ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        clbk( null, randu() > 0.5 );
    }
}

function done( error, result ) {
    if ( error ) {
        throw error;
    }
    console.log( result );
}

ifelseAsync( predicate, 1.0, -1.0, done );
```

The `predicate` function is provided a single argument:

-   `clbk`: callback to invoke upon `predicate` function completion.

The callback accepts two arguments:

-   `error`: error object.
-   `bool`: condition used to determine whether to return `x` or `y`.

The `done` callback is invoked upon function completion and is provided at most two arguments:

-   `error`: error object.
-   `result`: either `x` or `y`.

</section>

<!-- /.usage -->

<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

## 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`).

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

<!-- eslint-disable callback-return -->

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

```javascript
var randu = require( '@stdlib/random-base-randu' );
var ifelseAsync = require( '@stdlib/utils-async-if-else' );

var i;

function next() {
    ifelseAsync( predicate, 'BOOP', 'beep', done );
}

function predicate( clbk ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        clbk( null, randu() > 0.9 );
    }
}

function done( error, result ) {
    if ( error ) {
        throw error;
    }
    i += 1;
    console.log( result );
    if ( i < 100 ) {
        return next();
    }
}

i = 0;
next();
```

</section>

<!-- /.examples -->

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<section class="references">

</section>

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<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/utils-async/if-then`][@stdlib/utils/async/if-then]</span><span class="delimiter">: </span><span class="description">if a predicate function returns a truthy value, invoke `x`; otherwise, invoke `y`.</span>
-   <span class="package-name">[`@stdlib/utils-if-else`][@stdlib/utils/if-else]</span><span class="delimiter">: </span><span class="description">if a condition is truthy, return `x`; otherwise, return `y`.</span>

</section>

<!-- /.related -->

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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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<!-- <related-links> -->

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</section>

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