JavaScript set Interview Questions

A Set in JavaScript is a collection of unique values that maintains insertion order and removes duplicates automatically. It supports efficient operations like adding, deleting, and checking values, making it ideal for tasks involving uniqueness or deduplication. Unlike arrays, Set does not allow duplicate elements and provides methods like add(), delete(), and has() for easy manipulation.

We are going to discuss some Interview Questions related to set.

1. Explain the Set object in JavaScript.

A Set is a collection of unique values. Unlike arrays, duplicate values are not allowed. Even though 3 is repeated, Set stores only unique values.

const mySet = new Set([1, 2, 3, 3, 4]);
console.log(mySet);

Set(4) { 1, 2, 3, 4 }

2. Demonstrate how to add elements to a Set.

const mySet = new Set();
mySet.add(10);
mySet.add(20);
mySet.add(10); // Duplicate
console.log(mySet);

Set(2) { 10, 20 }

The .add() method adds elements to the Set, but duplicates are ignored.

3. Show how to remove a specific element from a Set.

const mySet = new Set([1, 2, 3]);
mySet.delete(2);
console.log(mySet);

Set(2) { 1, 3 }

Explanation: The .delete() method removes the specified value from the Set.

4. What is the difference between Set and Array?

5. Write code to check if a value exists in a Set.

const mySet = new Set([1, 2, 3, 4]);
console.log(mySet.has(3)); // true
console.log(mySet.has(5)); // false

true
false

6. Write code to convert a Set to an array.

const mySet = new Set([1, 2, 3]);
const myArray = Array.from(mySet);
console.log(myArray);

[ 1, 2, 3 ]

7. Write code to compute the union of two sets.

const setA = new Set([1, 2, 3]);
const setB = new Set([3, 4, 5]);
const union = new Set([...setA, ...setB]);
console.log(union);

Set(5) { 1, 2, 3, 4, 5 }

8. Write code to find common elements between two sets.

const setA = new Set([1, 2, 3]);
const setB = new Set([2, 3, 4]);
const intersection = new Set([...setA].filter(x => setB.has(x)));
console.log(intersection);

Set(2) { 2, 3 }

9. Write code to iterate over a Set.

const mySet = new Set(['a', 'b', 'c']);
for (const value of mySet) {
    console.log(value);
}

a
b
c

10. What will be the output?

const mySet = new Set();
mySet.add({ id: 1 });
mySet.add({ id: 1 }); 
console.log(mySet.size);

2

Explanation: A Set can store objects, but it treats different object references as unique.

11. Write code to clear all elements from a Set.

const mySet = new Set([1, 2, 3]);
mySet.clear();
console.log(mySet);

Set(0) {}

12. What will be the output?

const mySet = new Set();
mySet.add(1);
mySet.add("1");
mySet.add(1);
console.log(mySet.size);

Explanation: The Set treats 1 (number) and "1" (string) as different values. Although 1 is added twice, it is stored only once.

13. What will be the output?

const mySet = new Set(["apple", "banana", "apple", "cherry"]);
console.log([...mySet]);

14. What will be the output?

const mySet = new Set([NaN, NaN, "NaN"]);
console.log(mySet);

Explanation: In a Set, NaN is treated as equal to itself, even though NaN === NaN is false. "NaN" (string) is distinct from NaN.

15. What will be the output?

const mySet = new Set();
const obj = { id: 1 };
mySet.add(obj);
mySet.add({ id: 1 });
console.log(mySet.size);

Explanation: Each object has a unique reference. Even though both objects have the same properties, they are different objects.