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JavaScript error

SyntaxError

The JavaScript exception "octal escape sequences can't be used in untagged template literals or in strict mode code" occurs when octal escape sequences are used in strict mode string literals or untagged template literals.

Reference entryJavaScriptFetched
This is a reference entry from MDN Web Docs. A full explanation with fixes has not been written yet.

The error messages

SyntaxError: Octal escape sequences are not allowed in strict mode. (V8-based)
As listed by MDN Web Docs
SyntaxError: \8 and \9 are not allowed in strict mode. (V8-based)
As listed by MDN Web Docs
SyntaxError: Octal escape sequences are not allowed in template strings. (V8-based)
As listed by MDN Web Docs
SyntaxError: \8 and \9 are not allowed in template strings. (V8-based)
As listed by MDN Web Docs
SyntaxError: octal escape sequences can't be used in untagged template literals or in strict mode code (Firefox)
As listed by MDN Web Docs
SyntaxError: the escapes \8 and \9 can't be used in untagged template literals or in strict mode code (Firefox)
As listed by MDN Web Docs
SyntaxError: The only valid numeric escape in strict mode is '\0' (Safari)
As listed by MDN Web Docs

Details

Category
SyntaxError
Severity
error
Runtime
both

Related errors

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Source: MDN Web Docs. Data fetched 2026-09-25T01:48:37.273Z.