Typescript can not recognize when expression is callable

[ZhenyaUsenko]

Bug Report

Quick fix

🔎 Search Terms

Not all constituents of type are callable.

💻 Code

const getValue = <V>(value: V | (() => V)) =>
  typeof value === "function" ? value() : value;

🙁 Actual behavior

Error occurred

🙂 Expected behavior

Typescript should understand that expression is callable

[MartinJohns]

It would still not be safe, because V can be a function type.

Related / duplicate: #37663

[ZhenyaUsenko]

Yes, it can, but when typeof value === "function" returns true we are 100% sure value is callable

[MartinJohns]

But you are not sure if it's callable without any arguments. V can be of the type (arg: number) => void as well.

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.