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ifthenAsync

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

Installation

npm install @stdlib/utils-async-if-then

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md 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

var ifthenAsync = require( '@stdlib/utils-async-if-then' );

ifthenAsync( predicate, x, y, done )

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

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

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

function x( clbk ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        clbk( null, 1.0 );
    }
}

function y( clbk ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        clbk( null, -1.0 );
    }
}

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

ifthenAsync( predicate, x, y, 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 invoke x or y.

Both x and y are provided a single argument:

• clbk: callback to invoke upon function completion.

The callback function accepts any number of arguments, with the first argument reserved for providing an error. If the error argument is falsy, the done callback is invoked with its first argument as null and all other provided arguments. If the error argument is truthy, the done callback is invoked with only an error argument.

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

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

function x( clbk ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        clbk( null, 1.0, 2.0, 3.0 );
    }
}

function y( clbk ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        clbk( null, 4.0, 5.0, 6.0 );
    }
}

function done( error, a, b, c ) {
    if ( error ) {
        throw error;
    }
    console.log( a, b, c );
}

ifthenAsync( predicate, x, y, done );

Notes

• The function is similar to ifelseAsync(), but allows deferred argument evaluation.
• 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

var randu = require( '@stdlib/random-base-randu' );
var ceil = require( '@stdlib/math-base-special-ceil' );
var repeatString = require( '@stdlib/string-repeat' );
var ifthenAsync = require( '@stdlib/utils-async-if-then' );

var i;

function next() {
    ifthenAsync( predicate, x, y, done );
}

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

function x( clbk ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        clbk( null, repeatString( 'BOOP', ceil( randu()*3.0 ) ) );
    }
}

function y( clbk ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        clbk( null, repeatString( 'beep', ceil( randu()*5.0 ) ) );
    }
}

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

i = 0;
next();

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See Also

• @stdlib/utils-async/if-else: if a predicate function returns a truthy value, return x; otherwise, return y.
• @stdlib/utils-if-then: if a condition is truthy, invoke x; otherwise, invoke y.

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Notice

This package is part of 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, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2025. The Stdlib Authors.