Flatten a nested array. You must account for varying levels of nesting.

steamroller.js

function steamrollArray(arr) {
  // I'm a steamroller, baby
  var result = []; //store the resulting flat array
  //function to recursively flatten arrays inside of arrays.
  function flatten(arr){
    //for every item in the array check if it is an array itself
    for(var i = 0; i < arr.length; i++){
      if(Array.isArray(arr[i]) ){
        //if it is an array call the flatten function and concatinate the results
        //this will be called on all multidimensional arrays until flat
        result.concat(flatten(arr[i]));
      }
      else{
        //once flat add the item to the array
        result.push(arr[i]);
      }
    }
  }
  //call the function for the first time
  flatten(arr);
  return result;
}

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