JavaScript SyntaxError – “x” is not a legal ECMA-262 octal constant

This JavaScript warning 08 (or 09) is not a legal ECMA-262 octal constant that occurs if the literals 08 or 09 are used as a number. This occurs because these literals cannot be treated as an octal number.

Message:

Warning: SyntaxError: 08 is not a legal ECMA-262 octal constant.
Warning: SyntaxError: 09 is not a legal ECMA-262 octal constant.

Error Type:

Warning. JavaScript execution won't be halted.

Cause of Error: This happens when any of the digits after the leading 0 is equal to or greater than 8. This number cannot be treated as an octal number and therefore JavaScript gives a warning about it.

Example 1: In this example, the literal ’08’ gives a warning because it can not be interpreted as an octal number.

Javascript

"use strict";
// Error here
08;

Output:

Warning: SyntaxError: 08 is not a legal ECMA-262 octal constant.

Example 2: In this example, the literal ’09’ gives a warning because it can not be interpreted as an octal number.

Javascript

"use strict";
// Error here
09;

Output:

Warning: SyntaxError: 09 is not a legal ECMA-262 octal constant.