code: function maxBy(arr, fn) {
    if (!isArray(arr)) {
      return undefined;
    }
    var max = arr[0];
    var maxData = void 0;
    if (isFunction(fn)) {
      maxData = fn(arr[0]);
    } else {
      maxData = arr[0][fn];
    }
    var data = void 0;
    each(arr, function (val) {
      if (isFunction(fn)) {
        data = fn(val);
      } else {
        data = val[fn];
      }
      if (data > maxData) {
        max = val;
        maxData = data;
      }
    });
    return max;
  }
docs: @param {Array} arr The array to iterate over.
  @param {Function} [fn] The iteratee invoked per element.
  @return {*} Returns the maximum value.
  @example
  
  var objects = [{ 'n': 1 }, { 'n': 2 }];
  
  maxBy(objects, function(o) { return o.n; });
  // => { 'n': 2 }
  
  maxBy(objects, 'n');
  // => { 'n': 2 }