Flatten array. No matter the depth.

flatten.js

var flatten = function(){
  var reduce = function (array) {
    return array.reduce(function(r,e){
      return r.concat( (e instanceof Array) ? reduce(e) : e );
    },[]);    
  }
  return reduce(Array.prototype.slice.call(arguments));
}

flatten(1, 2, 3, [4, 5], [[[6]]], [7, [8, [9]]],10); // returns [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
flatten(["a","b"],[1,2,3],[null,[1,2,4]]); // returns ["a", "b", 1, 2, 3, null, 1, 2, 4]