SyntaxError: "x" is a reserved identifier

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

Message

SyntaxError: The use of a future reserved word for an identifier is invalid (Edge)
SyntaxError: "x" is a reserved identifier (Firefox)
SyntaxError: Unexpected reserved word (Chrome)

Error type

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
let
package
private
protected
public
static

Examples

Strict and non-strict reserved keywords

The enum identifier is generally reserved.

var enum = { RED: 0, GREEN: 1, BLUE: 2 };
// SyntaxError: enum is a reserved identifier

In strict mode code, more identifiers are reserved.

"use strict";
var package = ["potatoes", "rice", "fries"];
// SyntaxError: package is a reserved identifier

You'll need to rename these variables.

var colorEnum = { RED: 0, GREEN: 1, BLUE: 2 };
var list = ["potatoes", "rice", "fries"];

Update older browsers

If you are using an older browser that does not yet implement let or class, for example, you should update to a more recent browser version that does support these new language features.

"use strict";
class DocArchiver {}

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