code: function append(baseArr, value) {
      if (Array.isArray(value)) {
          baseArr.push.apply(baseArr, value);
      } else {
          baseArr.push(value);
      }
      return baseArr.length;
  }
docs: Append one or more values to the end of `baseArr`.
  Acts the same as `baseArr.concat(value)` but mutates instead of returning a copy.