Flatten array

flatten_array.js

function flatten(arr){
  var result = [];
  
  // If arr not an array, then just return it
  if(!isArray(arr))return arr;

  for(var i = 0, len = arr.length; i < len; i++){
    var flattened = flatten(arr[i]);
    if(isArray(flattened)){
      for(var j = 0, jlen = flattened.length; j < jlen; j++){
        // Could also use push()
        result.push(flattened[j]);
      }
    }
    else{
      result.push(flattened);
    }
//     result.concat(flatten(arr[i]));
  }
  return result;
}

function isArray(arr){
  return Object.prototype.toString.call(arr) === '[object Array]';
}

// flatten([[1,2,[3]],4, [6, [7, [8, [9, 10, [11, 12, 13]]]]]]);