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# resolveParentPathBy [![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] > Resolve a path according to a predicate function by walking parent directories.
## Installation ```bash npm install @stdlib/fs-resolve-parent-path-by ```
## Usage ```javascript var resolveParentPathBy = require( '@stdlib/fs-resolve-parent-path-by' ); ``` #### resolveParentPathBy( path\[, options], predicate, clbk ) Asynchronously resolves a path according to a `predicate` function by walking parent directories. ```javascript resolveParentPathBy( 'package.json', predicate, onPath ); function predicate( path, next ) { var bool = ( /\/test\//.test( path ) === false ); next( null, bool ); } function onPath( error, path ) { if ( error ) { throw error; } console.log( path ); // e.g., => '...' } ``` The function accepts the following `options`: - **dir**: base directory from which to begin walking. May be either an absolute path or a path relative to the current working directory. By default, the function begins walking from the current working directory. To specify an alternative directory, set the `dir` option. ```javascript var opts = { 'dir': __dirname }; resolveParentPathBy( 'package.json', opts, predicate, onPath ); function predicate( path, next ) { var bool = ( /\/test\//.test( path ) === false ); next( null, bool ); } function onPath( error, path ) { if ( error ) { throw error; } console.log( path ); // e.g., => '...' } ``` When invoked, the `predicate` function is provided two arguments: - **path**: a resolved path. - **next**: a callback which should be called once the `predicate` function has finished processing a resolved path. If a `predicate` function calls the `next` callback with a truthy second argument, the function stops processing any additional paths and returns the resolved path as the test result. If unable to resolve a path, the function returns `null` as the path result. #### resolveParentPathBy.sync( path\[, options], predicate ) Synchronously resolves a path according to a `predicate` function by walking parent directories. ```javascript function predicate( path ) { return ( /\/test\//.test( path ) === false ); } var path = resolveParentPathBy.sync( 'package.json', predicate ); // e.g., returns '...' ``` The function accepts the same `options` as [`resolveParentPathBy()`](#resolve-parent-path-by). When invoked, the `predicate` function is provided one argument: - **path**: a resolved path. The function immediately returns upon encountering a truthy `predicate` function return value. If unable to resolve a path, the function returns `null` as the path result.
## Notes - If a provided `predicate` function calls the `next` callback with a truthy `error` argument, the function suspends execution and immediately calls the `done` callback for subsequent `error` handling. - For `resolveParentPathBy`, 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`). - This implementation is **not** similar in functionality to core [`path.resolve`][node-core-path-resolve]. The latter performs string manipulation to generate a full path. This implementation walks parent directories to perform a **search**, thereby touching the file system. Accordingly, this implementation resolves a _real_ absolute file path and is intended for use when a target's location in a parent directory is unknown relative to a child directory; e.g., when wanting to find a package root from deep within a package directory.
## Examples ```javascript var resolveParentPathBy = require( '@stdlib/fs-resolve-parent-path-by' ); var opts = { 'dir': __dirname }; /* Sync */ function predicateSync( path ) { var pkg = require( path ); if ( pkg.name !== '@stdlib/stdlib' ) { return false; } return true; } var out = resolveParentPathBy.sync( 'package.json', opts, predicateSync ); console.log( out ); // e.g., => '...' out = resolveParentPathBy.sync( 'non_existent_basename/package.json', predicateSync ); console.log( out ); // => null /* Async */ function predicateAsync( path, next ) { setTimeout( onTimeout, 0 ); function onTimeout() { var pkg = require( path ); if ( pkg.name !== '@stdlib/stdlib' ) { return next( null, false ); } next( null, true ); } } function onPath( error, path ) { if ( error ) { throw error; } console.log( path ); } resolveParentPathBy( 'package.json', opts, predicateAsync, onPath ); resolveParentPathBy( './../non_existent_path/package.json', predicateAsync, onPath ); ```
* * * ## See Also - [`@stdlib/fs-resolve-parent-path`][@stdlib/fs/resolve-parent-path]: resolve a path by walking parent directories.
* * * ## Notice This package is part of [stdlib][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][stdlib], see the main project [repository][stdlib]. #### Community [![Chat][chat-image]][chat-url] --- ## License See [LICENSE][stdlib-license]. ## Copyright Copyright © 2016-2026. The Stdlib [Authors][stdlib-authors].
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