The JavaScript strict mode-only exception "0-prefixed octal literals and octal escape sequences are deprecated; for octal literals use the "0o" prefix instead" occurs when deprecated octal literals and octal escape sequences are used.
Message
SyntaxError: Octal numeric literals and escape characters not allowed in strict mode (Edge) SyntaxError: "0"-prefixed octal literals and octal escape sequences are deprecated; for octal literals use the "0o" prefix instead
Error type
SyntaxError in strict mode only.
What went wrong?
Octal literals and octal escape sequences are deprecated and will throw a SyntaxError in strict mode. With ECMAScript 2015 and later, the standardized syntax uses a leading zero followed by a lowercase or uppercase Latin letter "O" (0o or 0O).
Examples
"0"-prefixed octal literals
"use strict"; 03; // SyntaxError: "0"-prefixed octal literals and octal escape sequences // are deprecated
Octal escape sequences
"use strict"; "\251"; // SyntaxError: "0"-prefixed octal literals and octal escape sequences // are deprecated
Valid octal numbers
Use a leading zero followed by the letter "o" or "O":
0o3;
For octal escape sequences, you can use hexadecimal escape sequences instead:
'\xA9';