Is Check if Object Instance of Class easy or hard?

The problem is rated Medium because the concept appears simple but understanding how instance checks work internally can be tricky. The optimal solution is short using built-in operators, but explaining prototype traversal or inheritance mechanics requires deeper knowledge.

Check if Object Instance of Class Python/Java solution

Python solves the problem using isinstance(obj, ClassName), which checks the object's type and its parent classes. Java uses the instanceof operator, which returns true if the object belongs to the class or any subclass in its inheritance hierarchy.

How to solve Check if Object Instance of Class in O(1)?

Use the language's native instance checking operator. For example, JavaScript uses obj instanceof ClassName, Python uses isinstance(obj, ClassName), and Java also supports instanceof. These operations directly verify type relationships and run in constant time with no extra space.

What is the best approach for Check if Object Instance of Class?

The best approach is to use the language’s built-in instance checking feature such as JavaScript's instanceof, Python's isinstance(), Java's instanceof, or C#'s is operator. These are optimized runtime checks that verify whether the object's inheritance chain contains the given class. They run in O(1) time and require no additional memory.

Is Check if Object Instance of Class asked at Google/Amazon/Meta?

Problems involving type checking and object inheritance appear in interviews at companies that emphasize JavaScript or object-oriented fundamentals. Variants of prototype chain questions and instanceof behavior have been discussed in interviews at companies like Meta and frontend-heavy roles at large tech firms.

What data structure is used in Check if Object Instance of Class?

The core concept relies on the class inheritance hierarchy or prototype chain. In JavaScript this is implemented through linked prototype references between objects, forming a chain that can be traversed until the root object is reached.

What is the time complexity of Check if Object Instance of Class?

Using built-in instance checking typically runs in O(1) time with O(1) space because the runtime directly inspects the object's type information. A manual prototype-chain traversal solution in JavaScript takes O(h) time where h is the height of the prototype chain.

Description Hints 4 Solution Video 11:58

2618. Check if Object Instance of Class

Medium27.7% acceptance2 companies

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.

Example 1:

Input: func = () => checkIfInstanceOf(new Date(), Date)
Output: true
Explanation: The object returned by the Date constructor is, by definition, an instance of Date.

Example 2:

Input: func = () => { class Animal {}; class Dog extends Animal {}; return checkIfInstanceOf(new Dog(), Animal); }
Output: true
Explanation:
class Animal {};
class Dog extends Animal {};
checkIfInstanceOf(new Dog(), Animal); // true

Dog is a subclass of Animal. Therefore, a Dog object is an instance of both Dog and Animal.

Example 3:

Input: func = () => checkIfInstanceOf(Date, Date)
Output: false
Explanation: A date constructor cannot logically be an instance of itself.

Example 4:

Input: func = () => checkIfInstanceOf(5, Number)
Output: true
Explanation: 5 is a Number. Note that the "instanceof" keyword would return false. However, it is still considered an instance of Number because it accesses the Number methods. For example "toFixed()".

Asked at 2 companies

Google Microsoft

Hints open one at a time

Hint 1

In Javascript, inheritance is achieved with the prototype chain.

Hint 2

You can get the prototype of an object with the Object.getPrototypeOf(obj) function. Alternatively, you can code obj['__proto__'].

Hint 3

You can compare an object's __proto__ with classFunction.prototype.

Hint 4

Traverse the entire prototype chain until you find a match.

11:58

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LanguageLoading editor…

1/**
2 * @param {*} obj
3 * @param {*} classFunction
4 * @return {boolean}
5 */
6var checkIfInstanceOf = function(obj, classFunction) {
7    
8};
9 
10/**
11 * checkIfInstanceOf(new Date(), Date); // true
12 */

Starter codeJavaScriptSpaces: 4

Examples

Case 1Case 2Case 3Case 4

Input

() => checkIfInstanceOf(new Date(), Date)

Input

() => { class Animal {}; class Dog extends Animal {}; return checkIfInstanceOf(new Dog(), Animal); }

Input

() => checkIfInstanceOf(Date, Date)

Input

() => checkIfInstanceOf(5, Number)

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