dependency on @types/express-serve-static-core induced incompatibility

[alanpurple]

Environment information

Version:
express 5.2.1
@types/express 5.0.6

Platform:
windows 11 x64 and ubuntu 24.04.3

Node.js version:
24.13.0

Any other relevant information:

What steps will reproduce the bug?

currently express typing have dependency
"@types/express-serve-static-core": "^5.0.0",

which installs @types/express-serve-static-core 5.1.1, which is incompatible
works up to 5.1.0

so massive same errors like this

error TS2345: Argument of type 'string | string[]' is not assignable to parameter of type 'string'.
  Type 'string[]' is not assignable to type 'string'.

80         const id = parseInt(req.params.id);

generated

and this makes the documentation on
https://expressjs.com/en/5x/api.html
useless, in that documentation, same "req.params.id" is used

@types/express-serve-static-core should be fixed

[krzysdz]

The TypeScript type definitions for Express are maintained as a part of the DefinitelyTyped project and generally I'd suggest asking there about problems with @types/ packages.

The reason why your code broke is my recent PR DefinitelyTyped/DefinitelyTyped#74161 that fixed the req.params type. Your problems are not caused by a package version mismatch. In Express 5, if you use a path with a wildcard, the parameter that you get is an array. This is documented in the migration guide and req.params docs.

If you use a specific path with parameters, the typings will try to parse it and set the correct req.params type - e.g.:

app.get("/user/:id", (req, res) => {
    req.params.id // string
}

app.get("/file/*path", (req, res) => {
    req.params.path // string[]
}

If you don't give any path, then the default type - string | string[], which covers all possible types, will be used:

const handler: RequestHandler = (req, res) => {
    req.params.id // string | string[]
}

You can also declare the type of req.params yourself:

const handler1: RequestHandler<{ id: string }> = (req, res) => {
    req.params.id // string
}

const handler2 = (req: Request<{ path: string[] }>, res: Response) => {
    req.params.path // string[]
}