typescript: cannot apply parseInt() to a string in HTTP request header

Question

In typescript, I try to get an attribute from the http request header.

The attribute is a string (of course, it is from the header), I need to parse it into Integer

export const getUser =  async (req, _res, next) => {
  
  const userId: number = parseInt(req.headers.userid);
  
  ... other code 
}

However, the vs code IDE is displaying red line under req.headers.userid and complaining:

(property) IncomingMessage.headers: IncomingHttpHeaders
Argument of type 'string | string[] | undefined' is not assignable to parameter of type 'string'.
  Type 'undefined' is not assignable to type 'string'.ts(2345)

How can I do this simple task?

Show some more code or even playground link

Alireza Ahmadi
– Alireza Ahmadi

2021-08-06 17:01:28 +00:00
Commented Aug 6, 2021 at 17:01 — Alireza Ahmadi
– Alireza Ahmadi, Commented Aug 6, 2021 at 17:01

Alex Wayne · Accepted Answer · 2021-08-06 16:43:52Z

1

That error message says your variable is typed string | string[] | undefined, but parseInt requires string. So you have to handle the other types that userid could be.

Maybe something like:

const userIdHeader = req.headers.userid
if (typeof userIdHeader === 'string') {
  const userId = parseInt(userIdHeader);
}

Now you can only reach that code in the case where you have a string, and typescript knows it.

So the docs on narrowing for more info.

answered Aug 6, 2021 at 16:43

Alex Wayne

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Comments

Kid_Learning_C · Accepted Answer · 2021-10-15 17:31:24Z

0

I just had the exact same problem and I solved by:

const userIdHeader = req.headers.userid;
const userId = parseInt(String(userIdHeader));

Or better:

const userId = parseInt(String(req.headers.userid));

answered Oct 15, 2021 at 17:31

Kid_Learning_C

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