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Test whether a collection contains at least
nelements which pass a test implemented by a predicate function, iterating from right to left.
npm install @stdlib/utils-async-some-by-rightAlternatively,
- To load the package in a website via a
scripttag without installation and bundlers, use the ES Module available on theesmbranch (see README). - If you are using Deno, visit the
denobranch (see README for usage intructions). - For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the
umdbranch (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.
var someByRightAsync = require( '@stdlib/utils-async-some-by-right' );Tests whether a collection contains at least n elements which pass a test implemented by a predicate function, iterating from right to left.
function predicate( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
/* =>
1000
2500
3000
*/
next( null, false );
}
}
function done( error, bool ) {
if ( error ) {
throw error;
}
console.log( bool );
// => false
}
var arr = [ 1000, 2500, 3000 ];
someByRightAsync( arr, 2, predicate, done );The function immediately stops processing collection elements and returns true for the test result upon receiving n truthy predicate result values.
function predicate( value, index, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
if ( index === 1 ) {
return next( new Error( 'beep' ) );
}
next( null, true );
}
}
function done( error, bool ) {
if ( error ) {
throw error;
}
console.log( bool );
// => true
}
var arr = [ 1000, 2500, 3000 ];
someByRightAsync( arr, 1, predicate, done );The function accepts the following options:
limit: the maximum number of pending invocations at any one time. Default:infinity.series:booleanindicating whether to sequentially invoke thepredicatefunction for eachcollectionelement. Iftrue, the function setsoptions.limit=1. Default:false.thisArg: the execution context forpredicate.
By default, all elements are processed concurrently, which means that the function does not guarantee completion order. To process each collection element sequentially, set the series option to true.
function predicate( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
/* =>
3000
2500
1000
*/
next( null, false );
}
}
function done( error, bool ) {
if ( error ) {
throw error;
}
console.log( bool );
// => false
}
var arr = [ 1000, 2500, 3000 ];
var opts = {
'series': true
};
someByRightAsync( arr, 2, opts, predicate, done );To limit the maximum number of pending function invocations, set the limit option.
function predicate( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
/* =>
2500
3000
1000
*/
next( null, false );
}
}
function done( error, bool ) {
if ( error ) {
throw error;
}
console.log( bool );
// => false
}
var arr = [ 1000, 2500, 3000 ];
var opts = {
'limit': 2
};
someByRightAsync( arr, 2, opts, predicate, done );To set the execution context of the predicate function, set the thisArg option.
function predicate( value, next ) {
this.count += 1;
setTimeout( onTimeout, value );
function onTimeout() {
next( null, false );
}
}
var arr = [ 1000, 2500, 3000 ];
var context = {
'count': 0
};
var opts = {
'thisArg': context
};
someByRightAsync( arr, 2, opts, predicate, done );
function done( error, bool ) {
if ( error ) {
throw error;
}
console.log( bool );
// => false
console.log( context.count );
// => 3
}When invoked, the predicate function is provided a maximum of four arguments:
value: collection value.index: collection index.collection: the inputcollection.next: a callback which should be called once thepredicatefunction has finished processing a collectionvalue.
The actual number of provided arguments depends on function length. If the predicate function accepts two arguments, the predicate function is provided value and next. If the predicate function accepts three arguments, the predicate function is provided value, index, and next. For every other predicate function signature, the predicate function is provided all four arguments.
function predicate( value, i, collection, next ) {
console.log( 'collection: %s. %d: %d', collection.join( ',' ), i, value );
/* =>
collection: 3000,2500,1000. 2: 3000
collection: 3000,2500,1000. 1: 2500
collection: 3000,2500,1000. 0: 1000
*/
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
/* =>
1000
2500
3000
*/
next( null, false );
}
}
function done( error, bool ) {
if ( error ) {
throw error;
}
console.log( bool );
// => false
}
var arr = [ 1000, 2500, 3000 ];
someByRightAsync( arr, 2, predicate, done );Returns a function which invokes a predicate function once for each element in a collection, iterating from right to left.
function predicate( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next( null, false );
}
}
function done( error, bool ) {
if ( error ) {
throw error;
}
console.log( bool );
}
var f = someByRightAsync.factory( predicate );
var arr1 = [ 1000, 2500, 3000 ];
f( arr1, 2, done );
/* e.g., =>
1000
2500
3000
false
*/
var arr2 = [ 100, 250, 300 ];
f( arr2, 2, done );
/* e.g., >
100
250
300
false
*/The function accepts the same options as someByRightAsync().
- A
collectionmay be either anArray,Typed Array, or an array-likeObject(excludingstringsandfunctions). - If a provided function calls the
nextcallback with a truthyerrorargument, the function suspends execution and immediately calls thedonecallback for subsequenterrorhandling. - The function does not support dynamic
collectionresizing. - The function does not skip
undefinedelements. - If provided an empty
collection, the function calls thedonecallback withfalseas the test result. - Neither
someByRightAsyncnor the function returned by thefactorymethod guarantee asynchronous execution. To guarantee asynchrony, wrap thedonecallback 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).
var resolve = require( 'path' ).resolve;
var readFile = require( '@stdlib/fs-read-file' );
var someByRightAsync = require( '@stdlib/utils-async-some-by-right' );
var files = [
resolve( __dirname, 'package.json' ),
resolve( __dirname, 'README.md' )
];
function done( error, bool ) {
if ( error ) {
throw error;
}
if ( bool ) {
console.log( 'Successfully read some files.' );
} else {
console.log( 'Unable to read some files.' );
}
}
function predicate( file, next ) {
var opts = {
'encoding': 'utf8'
};
readFile( file, opts, onFile );
function onFile( error ) {
if ( error ) {
return next( null, false );
}
next( null, true );
}
}
someByRightAsync( files, 2, predicate, done );@stdlib/utils-async/any-by-right: test whether at least one element in a collection passes a test implemented by a predicate function, iterating from right to left.@stdlib/utils-async/every-by-right: test whether all elements in a collection pass a test implemented by a predicate function, iterating from right to left.@stdlib/utils-async/for-each-right: invoke a function once for each element in a collection, iterating from right to left.@stdlib/utils-async/none-by-right: test whether all elements in a collection fail a test implemented by a predicate function, iterating from right to left.@stdlib/utils-async/some-by: test whether a collection containsnelements which pass a test implemented by a predicate function.@stdlib/utils-some-by-right: test whether a collection contains at leastnelements which pass a test implemented by a predicate function, iterating from right to left.
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.
See LICENSE.
Copyright © 2016-2025. The Stdlib Authors.
