How to trigger Typescript type error for a function that expects some specific type and receives "any"?

Question

type CUSTOM_REQUEST = {
    someProp: "someValue"
}

const foo = (req: CUSTOM_REQUEST, err: unknown) => {
    console.log(req);
    console.log(err);
};

const someFunction = (req: CUSTOM_REQUEST) => {
    try {
        console.log("ON TRY");
    }
    catch(err) {
        foo(req,err);       // THIS IS OK
        foo(err,req);       // !!! THIS SHOULD NOT BE OK !!!
    }
};

The 2nd call of foo() has got the parameters reversed. And no type errors are being shown.

Second argumennt should be unknown and req: CUSTOM_REQUEST is being passed. That's ok.

But first argument should be req: CUSTOM_REQUEST and err:any is being passed. That should trigger an error, right?

How can I make sure Typescript alert me of this error?

Nicholas Tower · Accepted Answer · 2021-02-11 18:06:48Z

2

If something has type any, then it will never show a type error, since any basically disables type checking. So if you want to get a type error, then you'll need to have something other than an any

If you're running typescript 4.0 or later, you can give the err variable the type unknown instead of any:

catch (err: unknown) {
  foo(req,err); // Still ok
  foo(err,req); // Now shows an error, as expected
}

If you want to make sure you always tag your errors as unknown, typescript-eslint has a rule to enforce this: no-implicit-any-catch

answered Feb 11, 2021 at 18:06

Nicholas Tower

87k10 gold badges115 silver badges127 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How to trigger Typescript type error for a function that expects some specific type and receives "any"?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related