someByRightAsync

Usage

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.

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: 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.

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 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.

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.

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().