Question

I have:

var array1 = [];
var array2 = [];

array1 contains 1,2

array2 contains 3,4

And I want to do this:

for(var a in array1){
    for(var b in array2){
         doSomething(array1[a],array2[b]);
    }
}

But the problem is that function doSomething() runs twice for each array because of the two for‘s.

How should run it just once but with all of the arrays?

EDIT

The numbers are not in ascending order! In my real project they are ID‘s what can be any number in any order.

Answer 1

You shouldn’t use for..in for looping through arrays. Use an index variable:

for (var i = 0, len = array1.length; i < len; i++) {
    doSomething(array1[i], array2[i]);
}

This of course assumes they’re the same length.