Check if object instance of class

29.1% acceptance

Mar 2, 2026

293

111

Write a function that checks if a given value is an instance of a given class or superclass. For this problem, an object is considered an instance of a given class if that object has access to that class's methods. There are no constraints on the data types that can be passed to the function. For example, the value or the class could be undefined.

Solution

TypeScript

Time O(n)

Space O(1)

LeetCode

solution.ts

function checkIfInstanceOf(obj: any, classFunction: any): boolean {
  if (
  obj === null ||
  obj === undefined ||
  classFunction === null ||
  classFunction === undefined
  ) {
  return false;
  }
  let proto = Object.getPrototypeOf(Object(obj));
  while (proto !== null) {
  if (proto === classFunction.prototype) return true;
  proto = Object.getPrototypeOf(proto);
  }
  return false;
}

/**
 * checkIfInstanceOf(new Date(), Date); // true
 */