flattening the array

flatten.js

function steamroller(arr) {
  // I'm a steamroller, baby
  return flatten(arr);
}

function flatten(a, r){
    if(!r){ r = [];}
    for(var i=0; i<a.length; i++){
        if(Array.isArray(a[i])){
            flatten(a[i], r);
        }else{
            r.push(a[i]);
        }
    }
    return r;
}


steamroller([1, [2], [3, [[4]]]]);