JavaScript 的保留字 (reserved word) 包括關鍵字 (keyword) 、未來保留字 (future reserved word) 、三個字面常數 (literal) ,分別是 null 、 true 、 false 。
關鍵字為具有語法功能的標記,如下表
| break | delete | function | return | typeof |
| case | do | if | switch | var |
| catch | else | in | this | void |
| continue | finally | instanceof | throw | while |
| default | for | new | try | with |
| let |
未來保留字為將來有打算列入關鍵字之中的,如下表
| abstract | double | implements | private | throws |
| boolean | enum | import | protected | transient |
| byte | export | int | public | volatile |
| char | extends | interface | short | |
| class | final | long | static | |
| const | float | native | super | |
| debugger | goto | package | synchronized |