@stdlib/utils-async-for-each
v0.2.2
Published
Invoke a function once for each element in a collection.
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forEachAsync
Invoke a function once for each element in a collection.
Installation
npm install @stdlib/utils-async-for-each
Usage
var forEachAsync = require( '@stdlib/utils-async-for-each' );
forEachAsync( collection, [options,] fcn, done )
Invokes a function once for each element in a collection
.
function onDuration( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next();
}
}
function done( error ) {
if ( error ) {
throw error;
}
}
var arr = [ 3000, 2500, 1000 ];
forEachAsync( 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
fcn
for eachcollection
element. 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 = [ 3000, 2500, 1000 ];
var opts = {
'series': true
};
forEachAsync( 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 = [ 3000, 2500, 1000 ];
var opts = {
'limit': 2
};
forEachAsync( 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 = [ 3000, 2500, 1000 ];
var context = {
'count': 0
};
var opts = {
'thisArg': context
};
forEachAsync( 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
fcn
has 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 = [ 3000, 2500, 1000 ];
forEachAsync( arr, onDuration, done );
/* =>
collection: 3000,2500,1000. 0: 3000
collection: 3000,2500,1000. 1: 2500
collection: 3000,2500,1000. 2: 1000
1000
2500
3000
*/
forEachAsync.factory( [options,] fcn )
Returns a function which invokes a function once for each element in a collection
.
function onDuration( value, next ) {
setTimeout( onTimeout, value );
function onTimeout() {
console.log( value );
next();
}
}
function done( error ) {
if ( error ) {
throw error;
}
}
var f = forEachAsync.factory( onDuration );
var arr1 = [ 3000, 2500, 1000 ];
f( arr1, done );
/* =>
1000
2500
3000
*/
var arr2 = [ 300, 250, 100 ];
f( arr2, done );
/* =>
100
250
300
*/
The function accepts the same options
as forEachAsync()
.
Notes
- A
collection
may be either anArray
,Typed Array
, or an array-likeObject
(excludingstrings
andfunctions
). - If a provided function calls the
next
callback with a truthyerror
argument, the function suspends execution and immediately calls thedone
callback for subsequenterror
handling. - The function does not support dynamic
collection
resizing. - The function does not skip
undefined
elements. - Neither
forEachAsync
nor the function returned by thefactory
method guarantee asynchronous execution. To guarantee asynchrony, wrap thedone
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
var resolve = require( 'path' ).resolve;
var readFile = require( '@stdlib/fs-read-file' );
var forEachAsync = require( '@stdlib/utils-async-for-each' );
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();
}
}
forEachAsync( files, read, done );
See Also
@stdlib/utils-for-each
: invoke a function for each element in a collection.@stdlib/utils-async/for-each-right
: invoke a function once for each element in a collection, iterating from right to left.
Notice
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.
Community
License
See LICENSE.
Copyright
Copyright © 2016-2024. The Stdlib Authors.