stdlib-js
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</summary>
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someByRightAsync
[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url]
Test whether a collection contains at least
nelements which pass a test implemented by a predicate function, iterating from right to left.
bash
npm install @stdlib/utils-async-some-by-right
javascript
var someByRightAsync = require( '@stdlib/utils-async-some-by-right' );
#### someByRightAsync( collection, n, [options,] predicate, done )
Tests whether a collection contains at least n elements which pass a test implemented by a predicate function, iterating from right to left.
javascript
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.
javascript
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: boolean indicating whether to sequentially invoke the predicate function for each collection element. If true, the function sets options.limit=1. Default: false.
- thisArg: the execution context for predicate.
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.
javascript
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.
javascript
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.
javascript
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 input collection.
- next: a callback which should be called once the predicate function has finished processing a collection value.
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.
javascript
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 );
#### someByRightAsync.factory( [options,] predicate )
Returns a function which invokes a predicate function once for each element in a collection, iterating from right to left.
javascript
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().
collection may be either an [Array][mdn-array], [Typed Array][mdn-typed-array], or an array-like [Object][mdn-object] (excluding strings and functions).
- If a provided function calls the next callback with a truthy error argument, the function suspends execution and immediately calls the done callback for subsequent error handling.
- The function does not support dynamic collection resizing.
- The function does not skip undefined elements.
- If provided an empty collection, the function calls the done callback with false as the test result.
- Neither someByRightAsync nor the function returned by the factory method guarantee asynchronous execution. 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).
javascript
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][@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][@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][@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][@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][@stdlib/utils/async/some-by]: test whether a collection contains n elements which pass a test implemented by a predicate function.
- [@stdlib/utils-some-by-right][@stdlib/utils/some-by-right]: test whether a collection contains at least n elements which pass a test implemented by a predicate function, iterating from right to left.
