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trythen

If a function does not throw, return the function return value; otherwise, return the return value of a second function.

Installation

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

trythen( x, y )

If a function x does not throw, returns the return value of x; otherwise, returns the return value of a second function y.

function x1() {
    return 1.0;
}

function x2() {
    throw new Error( 'beep' );
}

function y() {
    return -1.0;
}

var z = trythen( x1, y );
// returns 1.0

z = trythen( x2, y );
// returns -1.0

The function y is provided a single argument:

• error: the error thrown by x.

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

function x() {
    if ( randu() < 0.5 ) {
        throw new Error( 'beep' );
    }
    throw new TypeError( 'boop' );
}

function y( err ) {
    if ( err instanceof TypeError ) {
        return 'boops';
    }
    return 'beeps';
}

var z = trythen( x, y );
// returns <string>

Examples

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

var z;
var i;

function x() {
    if ( randu() < 0.9 ) {
        throw new Error( 'BOOP' );
    }
    return repeatString( 'BOOP', ceil( randu()*3.0 ) );
}

function y() {
    return repeatString( 'beep', ceil( randu()*5.0 ) );
}

for ( i = 0; i < 100; i++ ) {
    z = trythen( x, y );
    console.log( z );
}

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See Also

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

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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 © 2016-2024. The Stdlib Authors.