node.js async forEach two arrays

Question

I have an issue with async and two arrays.

I have two arrays

var arrayOne = new Array();
var arrayTwo = new Array();

I am currently trying to figure out how to do the following async style inside a waterfall:

... // some code
function (arrayOne, arrayTwo, callback) {
    // do stuff
    for(var i = 0; arrayOne.length > i; i++) {
        // do more stuff
        callback(e, arrayOne[i], arrayTwo[i]);
    }
}, 
function (valueOne, valueTwo, callback) {
... // more code

I tried using the async.foreach but it only applys to one array :/

ergo:

... // some code
function (arrayOne, arrayTwo, callback) {
    // do stuff
    forEach(arrayOne, function(valueOne, callback) {
        // do more stuff
    }, function(e){
        // do more stuff
        callback(e, valueOne, /* valueTwo???? */);
    });
}, 
function (valueOne, valueTwo, callback) {
... // more code

Answer 1

Loop over the length of the shortest array using async.times:

function task( a, b, next ) {
    setTimeout( function() {
        next( null, a + b );
    }, 1000 );
}

function work( a, b, done ) {
    async.times( Math.min( a.length, b.length ), function( i, next ) {
        task( a[i], b[i], next );
    }, done );
}

var a = [1, 1, 1, 1];
var b = [1, 1, 1];

work( a, b, function( err, result ) {
    console.log( 'result:', result );
});

console.log( 'continuing...' );

Answer 2

// async.map for 2 arrays should be like this:

function map(a, b, func, cb) {
    var results = [];
    var length = Math.min(a.length, b.length);
    var countdown = length; // count to 0

    for(var i=0; i < length; i++) {
        func(a[i], b[i], function (err, result) {
            results.push(result);
            countdown--;
            if(countdown === 0) {
                cb(null, results) // cb is call on last result
            }
        })
    }
}

// test

var a = [1,1,1];
var b = [2,2,2];

function sum(a, b, cb) {
    // simulate async with timeout
    setTimeout(function () {
        cb(null, a + b);
    }, 1000);
}

map(a, b, sum, function (err, results) {
    console.log(results);
})

ouput:

[ 3, 3, 3 ]

Answer 3

I think you're overthinking it:

function (arrayOne, arrayTwo, callback) {
    forEach(arrayOne, callback, function(){
       forEach(arrayTwo, callback);
    });
};