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About stdlib...

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!

ifthenAsync

NPM version Build Status Coverage Status

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

Usage

To use in Observable,

ifthenAsync = require( 'https://cdn.jsdelivr.net/gh/stdlib-js/utils-async-if-then@umd/browser.js' )

To vendor stdlib functionality and avoid installing dependency trees for Node.js, you can use the UMD server build:

var ifthenAsync = require( 'path/to/vendor/umd/utils-async-if-then/index.js' )

To include the bundle in a webpage,

<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stdlib-js/utils-async-if-then@umd/browser.js"></script>

If no recognized module system is present, access bundle contents via the global scope:

<script type="text/javascript">
(function () {
    window.ifthenAsync;
})();
</script>

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

<!DOCTYPE html>
<html lang="en">
<body>
<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stdlib-js/random-base-randu@umd/browser.js"></script>
<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stdlib-js/math-base-special-ceil@umd/browser.js"></script>
<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stdlib-js/string-repeat@umd/browser.js"></script>
<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stdlib-js/utils-async-if-then@umd/browser.js"></script>
<script type="text/javascript">
(function () {

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();

})();
</script>
</body>
</html>

See Also

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.

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License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.