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Invoke a function once for each element in a collection, iterating from right to left.
To use in Observable,
forEachRightAsync = require( 'https://cdn.jsdelivr.net/gh/stdlib-js/utils-async-for-each-right@umd/browser.js' )To vendor stdlib functionality and avoid installing dependency trees for Node.js, you can use the UMD server build:
var forEachRightAsync = require( 'path/to/vendor/umd/utils-async-for-each-right/index.js' )To include the bundle in a webpage,
<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stdlib-js/utils-async-for-each-right@umd/browser.js"></script>If no recognized module system is present, access bundle contents via the global scope:
<script type="text/javascript">
(function () {
window.forEachRightAsync;
})();
</script>Invokes a function once for each element in a collection, iterating from right to left.
function onDuration( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next();
}
}
function done( error ) {
if ( error ) {
throw error;
}
}
var arr = [ 1000, 2500, 3000 ];
forEachRightAsync( arr, onDuration, done );
/* =>
1000
2500
3000
*/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
fcnfor eachcollectionelement. Iftrue, the function setsoptions.limit=1. Default:false. - thisArg: the execution context for
fcn.
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 onDuration( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next();
}
}
function done( error ) {
if ( error ) {
throw error;
}
}
var arr = [ 1000, 2500, 3000 ];
var opts = {
'series': true
};
forEachRightAsync( arr, opts, onDuration, done );
/* =>
3000
2500
1000
*/To limit the maximum number of pending function invocations, set the limit option.
function onDuration( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next();
}
}
function done( error ) {
if ( error ) {
throw error;
}
}
var arr = [ 1000, 2500, 3000 ];
var opts = {
'limit': 2
};
forEachRightAsync( arr, opts, onDuration, done );
/* =>
2500
3000
1000
*/To set the execution context of fcn, set the thisArg option.
function onDuration( value, next ) {
this.count += 1;
setTimeout( onTimeout, value );
function onTimeout() {
next();
}
}
var arr = [ 1000, 2500, 3000 ];
var context = {
'count': 0
};
var opts = {
'thisArg': context
};
forEachRightAsync( arr, opts, onDuration, done );
function done( error ) {
if ( error ) {
throw error;
}
console.log( context.count );
// => 3
}When invoked, fcn 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
fcnhas finished processing a collectionvalue.
The actual number of provided arguments depends on function length. If fcn accepts two arguments, fcn is provided value and next. If fcn accepts three arguments, fcn is provided value, index, and next. For every other fcn signature, fcn is provided all four arguments.
function onDuration( value, i, collection, next ) {
console.log( 'collection: %s. %d: %d', collection.join( ',' ), i, value );
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next();
}
}
function done( error ) {
if ( error ) {
throw error;
}
}
var arr = [ 1000, 2500, 3000 ];
forEachRightAsync( arr, onDuration, done );
/* =>
collection: 3000,2500,1000. 2: 3000
collection: 3000,2500,1000. 1: 2500
collection: 3000,2500,1000. 0: 1000
1000
2500
3000
*/Returns a function which invokes a function once for each element in a collection, iterating from right to left.
function onDuration( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next();
}
}
function done( error ) {
if ( error ) {
throw error;
}
}
var f = forEachRightAsync.factory( onDuration );
var arr1 = [ 1000, 2500, 3000 ];
f( arr1, done );
/* =>
1000
2500
3000
*/
var arr2 = [ 100, 250, 300 ];
f( arr2, done );
/* =>
100
250
300
*/The function accepts the same options as forEachRightAsync().
- 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. - Neither
forEachRightAsyncnor 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).
<!DOCTYPE html>
<html lang="en">
<body>
<script type="text/javascript">
(function () {
var resolve = require( 'path' ).resolve;
var readFile = require( '@stdlib/fs-read-file' );
var forEachRightAsync = require( '@stdlib/utils-async-for-each-right' );
var files = [
resolve( __dirname, 'package.json' ),
resolve( __dirname, 'README.md' )
];
function done( error ) {
if ( error ) {
throw error;
}
console.log( 'Successfully read all files.' );
}
function read( file, next ) {
var opts = {
'encoding': 'utf8'
};
readFile( file, opts, onFile );
function onFile( error ) {
if ( error ) {
error = new Error( 'unable to read file: '+file );
return next( error );
}
console.log( 'Successfully read file: %s', file );
next();
}
}
forEachRightAsync( files, read, done );
})();
</script>
</body>
</html>@stdlib/utils-async/for-each: invoke a function once for each element in a collection.@stdlib/utils-for-each-right: invoke a function for each element in a collection, 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 © 2016-2024. The Stdlib Authors.