doUntilEachRight

Usage

var doUntilEachRight = require( '@stdlib/utils/do-until-each-right' );

doUntilEachRight( collection, fcn, predicate[, thisArg ] )

Invokes a function for each element in a collection, iterating from right to left, until either a predicate function returns true or the function has iterated over all collection elements. Note that the condition is evaluated after executing fcn; thus, fcn always executes at least once.

function predicate( value ) {
    return ( value !== value );
}

function log( value, index ) {
    console.log( '%s: %d', index, value );
}

var arr = [ 1, NaN, 2, 3, 4 ];

doUntilEachRight( arr, log, predicate );
/* =>
    4: 4
    3: 3
    2: 2
    1: NaN
*/

Both the predicate function and the function to apply are provided three arguments:

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

If provided an empty collection, both value and index are undefined.

function predicate( value ) {
    return ( value !== value );
}

function log( value, index ) {
    console.log( '%s: %s', index, value );
}

var arr = [];

doUntilEachRight( arr, log, predicate );
/* =>
    undefined: undefined
*/

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 predicate( value ) {
    return ( value !== value );
}

function log1( value, index, collection ) {
    console.log( '%s: %d', index, value );
    i += 1;
    if ( index === 0 && collection.length < 10 ) {
        collection.unshift( i+1 );
    }
}

doUntilEachRight( arr, log1, predicate );
/* =>
    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 ];

doUntilEachRight( arr, log2, predicate );
/* =>
    3: 4
    1: 2
*/

To set the function execution context for the applied function, provide a thisArg.

function predicate( value ) {
    return ( value < 3 );
}

function sum( value ) {
    this.sum += value;
    this.count += 1;
}

var arr = [ 1, NaN, 2, 3, 4 ];

var context = {
    'sum': 0,
    'count': 0
};

doUntilEachRight( arr, sum, predicate, context );

var mean = context.sum / context.count;
// returns 3.0