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JS
JavaScript error

SyntaxError

The JavaScript exception "missing formal parameter" occurs when your function declaration is missing valid parameters.

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: missing formal parameter (Firefox)
As listed by MDN Web Docs
SyntaxError: Unexpected number '3'. Expected a parameter pattern or a ')' in parameter list. (Safari)
As listed by MDN Web Docs
SyntaxError: Unexpected string literal "x". Expected a parameter pattern or a ')' in parameter list. (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 2026-09-25T01:48:37.274Z.