var lstOut = ['', '', ''];
[["a", "b", "c"], ["A", "B", "C"], ["1", "2", "3"]].forEach(
function (a) {
[0, 1, 2].forEach(
function (i) {
// side-effect on an array outside the function
lstOut[i] += a[i];
}
);
// lstOut --> ["aA1", "bB2", "cC3"]