SyntaxError: Octal literals are not allowed in strict mode. (V8-based)
SyntaxError: "0"-prefixed octal literals are deprecated; use the "0o" prefix instead (Firefox)
SyntaxError: Decimal integer literals with a leading zero are forbidden in strict mode (Safari)

SyntaxError: Octal escape sequences are not allowed in strict mode. (V8-based)
SyntaxError: octal escape sequences can't be used in untagged template literals or in strict mode code (Firefox)
SyntaxError: The only valid numeric escape in strict mode is '\0' (Safari)

SyntaxError in strict mode only.

Octal literals and octal escape sequences are deprecated and will throw a SyntaxError in strict mode. The standardized syntax uses a leading zero followed by a lowercase or uppercase Latin letter "O" (0o or 0O).

Use a leading zero followed by the letter "o" or "O":

0o3;

For octal escape sequences, you can use hexadecimal escape sequences instead:

"\xA9";

• Lexical grammar