@technobuddha/library/src/is-function.ts

A large library of useful functions

import { isObject } from './is-object.ts';

/**
 * Determines whether the provided value is a function.
 *
 * This includes regular functions, generator functions, async functions, and proxies
 * that behave like functions. It uses both `typeof` and `Object.prototype.toString`
 * checks to ensure accurate detection.
 * @param value - The value to test.
 * @returns True if the value is a function, otherwise false.
 * @group Object
 * @category Type Guards
 * @example
 * ```typescript
 * isFunction(function() {}); // true
 * isFunction(() => {}); // true
 * isFunction(async function() {}); // true
 * isFunction(function* () {}); // true
 * isFunction(null); // false
 * isFunction({}); // false
 * ```
 */
// eslint-disable-next-line @typescript-eslint/no-unsafe-function-type
export function isFunction(value: unknown): value is Function {
  return (
    typeof value === 'function' ||
    (isObject(value) &&
      [
        '[object Function]',
        '[object GeneratorFunction]',
        '[object AsyncFunction]',
        '[object Proxy]',
      ].includes(Object.prototype.toString.call(value)))
  );
}