forEachRight

    Invoke a function for each element in a collection, iterating from the right to left.

    Usage

    var forEachRight = require( '@stdlib/utils/for-each-right' );
    

    forEachRight( collection, fcn[, thisArg ] )

    Invokes a function for each element in a collection, iterating from right to left.

    function log( value, index ) {
        console.log( '%s: %d', index, value );
    }
    
    var arr = [ 1, 2, 3, 4 ];
    
    forEachRight( arr, log );
    /* =>
        3: 4
        2: 3
        1: 2
        0: 1
    */
    

    The invoked function is provided three arguments:

    • value: collection element
    • index: collection index
    • collection: input collection

    Basic support for dynamic collections is provided. Note, however, that index incrementation is not guaranteed to be monotonically decreasing.

    var arr = [ 1, 2, 3, 4 ];
    var i = 0;
    
    function log1( value, index, collection ) {
        console.log( '%s: %d', index, value );
        i += 1;
        if ( index === 0 && collection.length < 10 ) {
            collection.unshift( i+1 );
        }
    }
    
    forEachRight( arr, log1 );
    /* =>
        3: 4
        2: 3
        1: 2
        0: 1
        0: 5
        0: 6
        0: 7
        0: 8
        0: 9
        0: 10
    */
    
    function log2( value, index, collection ) {
        console.log( '%s: %d', index, value );
        collection.pop();
    }
    
    arr = [ 1, 2, 3, 4 ];
    
    forEachRight( arr, log2 );
    /* =>
        3: 4
        1: 2
    */
    

    To set the function execution context, provide a thisArg.

    function sum( value ) {
        this.sum += value;
        this.count += 1;
    }
    
    var arr = [ 1, 2, 3, 4 ];
    
    var context = {
        'sum': 0,
        'count': 0
    };
    
    forEachRight( arr, sum, context );
    
    var mean = context.sum / context.count;
    // returns 2.5
    

    Notes

    • A collection may be either an Array, Typed Array, or an array-like Object (excluding strings and functions).

    • The function differs from Array.prototype.forEach in the following ways:

      • The function returns the input collection.

      • The function does not skip undefined elements.

        function log( value, index ) {
            console.log( '%s: %s', index, value );
        }
        
        var arr = [ 1, , , 4 ];
        
        forEachRight( arr, log );
        /* =>
            3: 4
            2: undefined
            1: undefined
            0: 1
        */
        
      • The function provides limited support for dynamic collections (i.e., collections whose length changes during execution).

    Examples

    var isEven = require( '@stdlib/assert/is-even' ).isPrimitive;
    var forEachRight = require( '@stdlib/utils/for-each-right' );
    
    var arr;
    var i;
    
    function log( value, index, collection ) {
        console.log( '%s: %d', index, value );
        i += 1;
        if ( isEven( i ) ) {
            collection.pop();
        } else {
            collection.unshift( i+1 );
        }
    }
    
    arr = new Array( 100 );
    for ( i = arr.length-1; i >= 0; i-- ) {
        arr[ i ] = i;
    }
    
    i = 0;
    forEachRight( arr, log );