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JS
JavaScript error

SyntaxError

The JavaScript exception "await expression can't be used in parameter" or "yield expression can't be used in parameter" occurs when the default parameter expression contains the await or yield keyword and has the effect of pausing default parameter evaluation.

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: Illegal await-expression in formal parameters of async function (V8-based)
As listed by MDN Web Docs
SyntaxError: await expression can't be used in parameter (Firefox)
As listed by MDN Web Docs
SyntaxError: Cannot use 'await' within a parameter default expression. (Safari)
As listed by MDN Web Docs
SyntaxError: Yield expression not allowed in formal parameter (V8-based)
As listed by MDN Web Docs
SyntaxError: yield expression can't be used in parameter (Firefox)
As listed by MDN Web Docs
SyntaxError: Unexpected keyword 'yield'. Cannot use yield expression within parameters. (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.