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SyntaxError: "x" is a reserved identifier

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The JavaScript exception "variable is a reserved identifier" occurs when reserved keywords are used as identifiers.

Message#

SyntaxError: Unexpected reserved word (V8-based)
SyntaxError: implements is a reserved identifier (Firefox)
SyntaxError: Cannot use the reserved word 'implements' as a variable name. (Safari)

Error type#

{{jsxref("SyntaxError")}}

What went wrong?#

Reserved keywords will throw in if they are used as identifiers. These are reserved in strict mode and sloppy mode:

  • enum

The following are only reserved when they are found in strict mode code:

  • implements
  • interface
  • {{jsxref("Statements/let", "let")}}
  • package
  • private
  • protected
  • public
  • static

Examples#

Strict and non-strict reserved keywords#

The enum identifier is generally reserved.

```js-nolint example-bad const enum = { RED: 0, GREEN: 1, BLUE: 2 }; // SyntaxError: enum is a reserved identifier

In strict mode code, more identifiers are reserved.

```js-nolint example-bad
"use strict";
const package = ["potatoes", "rice", "fries"];
// SyntaxError: package is a reserved identifier

You'll need to rename these variables.

```js example-good const colorEnum = { RED: 0, GREEN: 1, BLUE: 2 }; const list = ["potatoes", "rice", "fries"];

### Update older browsers

If you are using an older browser that does not yet implement
[`let`](/en-US/docs/Web/JavaScript/Reference/Statements/let) or
[`class`](/en-US/docs/Web/JavaScript/Reference/Statements/class),
for example, you should update to a more recent browser version that does support these
new language features.

```js
"use strict";
class DocArchiver {}

// SyntaxError: class is a reserved identifier
// (throws in older browsers only, e.g. Firefox 44 and older)

See also#