stdlib-js/utils-async-try-then

If a function does not return an error, invoke a callback with the function result; otherwise, invoke a second function.

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!

trythenAsync

If a function does not return an error, invoke a callback with the function result; otherwise, invoke a second function.

Installation

npm install @stdlib/utils-async-try-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 trythenAsync = require( '@stdlib/utils-async-try-then' );

trythenAsync( x, y, done )

If a function x does not return an error, invokes a done callback with the function result; otherwise, invokes a second function y.

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

function x( clbk ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        if ( randu() > 0.5 ) {
            return clbk( null, 1.0 );
        }
        clbk( new Error( 'oops' ) );
    }
}

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

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

trythenAsync( x, y, done );

The function x is 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.

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

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 );
}

trythenAsync( x, y, done );

If the error argument is truthy, the function invokes y. The number of arguments provided to y depends on the function's length. If y is a unary function, y is provided a single argument:

• clbk: callback to invoke upon function completion

Otherwise, y is provided two arguments:

• error: the error from x
• 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 equal to null and all other provided arguments. If the error argument is truthy, the done callback is invoked with only the error argument provided by y.

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

function x( clbk ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        if ( randu() > 0.5 ) {
            return clbk( null, 1.0, 2.0, 3.0 );
        }
        clbk( new Error( 'beep' ) );
    }
}

function y( clbk ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        if ( randu() > 0.5 ) {
            return clbk( null, 4.0, 5.0, 6.0 );
        }
        clbk( new Error( 'boop' ) );
    }
}

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

trythenAsync( x, y, done );

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

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

var i;

function next() {
    trythenAsync( x, y, done );
}

function x( clbk ) {
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        if ( randu() > 0.9 ) {
            return clbk( null, repeatString( 'BOOP', ceil( randu()*3.0 ) ) );
        }
        clbk( new Error( 'oops' ) );
    }
}

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();

---

See Also

• @stdlib/utils-async/try-catch: if a function does not return an error, invoke a callback with the function result; otherwise, invoke a callback with a value y.
• @stdlib/utils-try-then: if a function does not throw, return the function return value; otherwise, return the return value of a second function.

---

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

---

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.