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# trythenAsync [![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] > If a function does not return an error, invoke a callback with the function result; otherwise, invoke a second function.
## Usage ```javascript import trythenAsync from 'https://cdn.jsdelivr.net/gh/stdlib-js/utils-async-try-then@esm/index.mjs'; ``` #### 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`. ```javascript import randu from 'https://cdn.jsdelivr.net/gh/stdlib-js/random-base-randu@esm/index.mjs'; 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. ```javascript import randu from 'https://cdn.jsdelivr.net/gh/stdlib-js/random-base-randu@esm/index.mjs'; 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`. ```javascript import randu from 'https://cdn.jsdelivr.net/gh/stdlib-js/random-base-randu@esm/index.mjs'; 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 ```html ```
* * * ## See Also - [`@stdlib/utils-async/try-catch`][@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`][@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][stdlib], a standard library 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 © 2016-2024. The Stdlib [Authors][stdlib-authors].
[npm-image]: http://img.shields.io/npm/v/@stdlib/utils-async-try-then.svg [npm-url]: https://npmjs.org/package/@stdlib/utils-async-try-then [test-image]: https://github.com/stdlib-js/utils-async-try-then/actions/workflows/test.yml/badge.svg?branch=main [test-url]: https://github.com/stdlib-js/utils-async-try-then/actions/workflows/test.yml?query=branch:main [coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/utils-async-try-then/main.svg [coverage-url]: https://codecov.io/github/stdlib-js/utils-async-try-then?branch=main [chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg [chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im [stdlib]: https://github.com/stdlib-js/stdlib [stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors [umd]: https://github.com/umdjs/umd [es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules [deno-url]: https://github.com/stdlib-js/utils-async-try-then/tree/deno [deno-readme]: https://github.com/stdlib-js/utils-async-try-then/blob/deno/README.md [umd-url]: https://github.com/stdlib-js/utils-async-try-then/tree/umd [umd-readme]: https://github.com/stdlib-js/utils-async-try-then/blob/umd/README.md [esm-url]: https://github.com/stdlib-js/utils-async-try-then/tree/esm [esm-readme]: https://github.com/stdlib-js/utils-async-try-then/blob/esm/README.md [branches-url]: https://github.com/stdlib-js/utils-async-try-then/blob/main/branches.md [stdlib-license]: https://raw.githubusercontent.com/stdlib-js/utils-async-try-then/main/LICENSE [@stdlib/utils/async/try-catch]: https://github.com/stdlib-js/utils-async-try-catch/tree/esm [@stdlib/utils/try-then]: https://github.com/stdlib-js/utils-try-then/tree/esm