How do I specify a callback function after rest parameters in TypeScript?

I have a function that receives an some arbitrary number of strings like in this example:

function foo(...strings, callback);

How do I specify it's types in typescript? I weighed the following alternatives:

functio foo(...strings: string, callback: (err: Error, res: any) => void);

this is no good because rest parameters have to be last.

foo(...strings: any);

this is a compromise that will compile but requires forfeiting type checking.

foo(...strings: string|((err: Error, res: any) => void));

this is a bit more true but is very non-readable and I don't think I saw it in any project.

Is there a best practice to deal with this? What trade offs should be taken into account?

You can't , only the last parameter can be a rest parameter. developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…
– vibhor1997a
Aug 19 at 13:45

Have you thought returning a promise/async instead? This way you don't have to cope with callback definition, and your code code would look nicer
– Mor Shemesh
Aug 19 at 13:51

Of course I'd rather change the api but is still the conventions in many libraries and I wish to edit a type file for such a library.
– Imri Paran
2 days ago

1 Answer
1

This is not possible, you have to change your 'order style', and put your callback before your rest parameters. That would be a better (more readable and more type safe) solution than the other awkward workarounds you listed.

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