http://www.freecodecamp.com/patrickcurl 's solution for Bonfire: Steamroller

bonfire-steamroller.js

// Bonfire: Steamroller
// Author: @patrickcurl
// Challenge: http://www.freecodecamp.com/challenges/bonfire-steamroller
// Learn to Code at Free Code Camp (www.freecodecamp.com)

function steamroller(arr) {
  // I'm a steamroller, baby
  var newArr = [];
  var flatten = function(x){
    if(!Array.isArray(x)){
      newArr.push(x);
    } else {
      for(var a in x){
        flatten(x[a]);
      }
    }
  };
  arr.forEach(flatten);
  return newArr;
}

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