Working with Sets

Question 1

How do you create a new, empty Set in JavaScript?

Answer 1

const mySet = new Set();

Question 2

How do you create a Set and initialize it with values from an existing array?

Answer 2

const myArray = [1, 2, 2, 3]; const mySet = new Set(myArray); // duplicates removed

Question 3

How do you add a new element to a Set?

Answer 3

mySet.add(value); // e.g., mySet.add(5);

Question 4

What happens if you try to add a duplicate value to a Set?

Answer 4

Duplicate values are ignored — Sets only store unique items.

Question 5

How do you remove an element from a Set?

Answer 5

mySet.delete(value); // e.g., mySet.delete(2);

Question 6

What is the return value of the delete() method in Sets?

Answer 6

true if removed successfully; false if element not found.

Question 7

How do you check if a Set contains a specific value?

Answer 7

mySet.has(value); // e.g., mySet.has(7);

Question 8

What is the return value of the has() method in Sets?

Answer 8

Boolean — true if the value exists, false otherwise.

Question 9

How do you remove all elements from a Set?

Answer 9

mySet.clear();

Question 10

How can you loop through all the values in a Set?

Answer 10

for (const value of mySet) { … } // or mySet.forEach(v => { … });

Question 11

Does a Set have indexes like an array?

Answer 11

No — Sets have no indexes; you can’t access by position.

Question 12

How do you convert a Set back into an array?

Answer 12

const myArray = […mySet];

Question 13

How can you efficiently remove duplicates from an array using Sets?

Answer 13

const uniqueArray = […new Set(myArrayWithDuplicates)];

Question 14

Are Sets guaranteed to maintain insertion order?

Answer 14

Yes — Sets preserve the order elements were added.

Question 15

How do you perform a union of two Sets (all unique elements)?

Answer 15

function setUnion(setA, setB) {
const unionSet = new Set(setA);
for (const elem of setB) unionSet.add(elem);
return unionSet;
}

Question 16

How do you perform an intersection of two Sets (common elements)?

Answer 16

function setIntersection(setA, setB) {
const intersectionSet = new Set();
for (const elem of setB)
if (setA.has(elem)) intersectionSet.add(elem);
return intersectionSet;
}

Question 17

How do you perform a difference of two Sets (A minus B)?

Answer 17

function setDifference(setA, setB) {
const differenceSet = new Set(setA);
for (const elem of setB) differenceSet.delete(elem);
return differenceSet;
}