@stdlib/utils-async-map-function NPM

mapFunAsync

Invoke a function n times and return an array of accumulated function return values.

Installation

npm install @stdlib/utils-async-map-function

Usage

var mapFunAsync = require( '@stdlib/utils-async-map-function' );

mapFunAsync( fcn, n, [options,] done )

Invokes a function n times and returns an array of accumulated function return values.

function fcn( i, next ) {
    var t = 300 - (i*50);
    setTimeout( onTimeout, t );
    function onTimeout() {
        console.log( i );
        next( null, i );
    }
}

function done( error, arr ) {
    if ( error ) {
        throw error;
    }
    console.log( arr );
}

mapFunAsync( fcn, 5, done );
/* =>
    4
    3
    2
    1
    0
    [ 0, 1, 2, 3, 4 ]
*/

For each iteration, the provided function is invoked with two arguments:

index: invocation index (starting from zero)
next: callback to be invoked upon function completion

The next callback accepts two arguments:

error: error argument
result: function result

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. If true, the function sets options.limit=1. Default: false.
thisArg: the execution context for fcn.

By default, all invocations are performed concurrently, which means that the function does not guarantee completion order. To invoke a function such that only one invocation is pending at any one time, set the series option to true.

function fcn( i, next ) {
    var t = 300 - (i*50);
    setTimeout( onTimeout, t );
    function onTimeout() {
        console.log( i );
        next( null, i );
    }
}

function done( error, arr ) {
    if ( error ) {
        throw error;
    }
    console.log( arr );
}

var opts = {
    'series': true
};

mapFunAsync( fcn, 5, opts, done );
/* =>
    0
    1
    2
    3
    4
    [ 0, 1, 2, 3, 4 ]
*/

To limit the maximum number of pending function invocations, set the limit option.

var delays = [ 300, 250, 225, 150, 100 ];

function fcn( i, next ) {
    setTimeout( onTimeout, delays[ i ] );
    function onTimeout() {
        console.log( i );
        next( null, i );
    }
}

function done( error, arr ) {
    if ( error ) {
        throw error;
    }
    console.log( arr );
}

var opts = {
    'limit': 2
};

mapFunAsync( fcn, 5, opts, done );
/* =>
    1
    0
    3
    2
    4
    [ 0, 1, 2, 3, 4 ]
*/

To set the execution context of fcn, set the thisArg option.

function fcn( i, next ) {
    this.count += 1;
    setTimeout( onTimeout, 0 );
    function onTimeout() {
        next( null, i );
    }
}

function done( error, arr ) {
    if ( error ) {
        throw error;
    }
    console.log( arr );
    // => [ 0, 1, 2, 3, 4 ]
}

var ctx = {
    'count': 0
};
var opts = {
    'thisArg': ctx
};

mapFunAsync( fcn, 5, opts, done );

mapFunAsync.factory( [options,] fcn )

Returns a function which invokes a function n times and returns an array of accumulated function return values.

function fcn( i, next ) {
    var t = 300 - (i*50);
    setTimeout( onTimeout, t );
    function onTimeout() {
        console.log( i );
        next( null, i );
    }
}

function done( error, arr ) {
    if ( error ) {
        throw error;
    }
    console.log( arr );
}

var opts = {
    'series': true
};

var f = mapFunAsync.factory( opts, fcn );

f( 5, done );
/* =>
    0
    1
    2
    3
    4
    [ 0, 1, 2, 3, 4 ]
*/

f( 2, done );
/* =>
    0
    1
    [ 0, 1 ]
*/

The function accepts the same options as mapFunAsync().

Notes

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.
Neither mapFunAsync 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).

Examples

var randu = require( '@stdlib/random-base-randu' );
var mapFunAsync = require( '@stdlib/utils-async-map-function' );

function rand( i, next ) {
    var t = randu() * i;
    setTimeout( onTimeout, t );
    function onTimeout() {
        next( null, t );
    }
}

function done( error, out ) {
    if ( error ) {
        throw error;
    }
    console.log( out );
}

mapFunAsync( rand, 10, done );

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.