This loops over the indices of the first array, and uses that to index into the others.

array.js

function loopMultipleArrays() {
  var a = ["a","b","c"];
  var b = ["A","B","C"];
  var c = [1,2,3];
  output = "";
  var i;
  for (i = 0; i < a.length; i += 1) {
    output += a[i] + b[i] + c[i] + "\n";
  }
}