code: function(arr, iterator, callback) {
        callback = _doOnce(callback || noop);
        var amount = arr.length;
  
        if (!isArray(arr)) return callback();
  
        var completed = 0;
        doEach(arr, function(item) {
          iterator(item, doOnce(function(err) {
            if (err) {
              callback(err);
              callback = noop;
            } else {
              completed++;
              if (completed >= amount) callback(null);
            }
          }));
        });
      }
docs: runs the task on every item in the array at once