isFunction

Problem

You need to check whether a value is callable — for example accepting either a static value or a factory function.

Solution

Use isFunction(value) to narrow to (...args: unknown[]) => unknown.

import { isFunction } from '@vielzeug/arsenal';

function resolve<T>(valueOrFactory: T | (() => T)): T {
  return isFunction(valueOrFactory) ? valueOrFactory() : valueOrFactory;
}

resolve(42); // 42
resolve(() => 42); // 42

Related

• isPromise