JS 2025

Question 1

What’s the best way to clone an Object?

Answer 1

structuredClone(objectName)

alternative: JSON.parse(JSON.stringify(objectName) and assign to a new object (=)

Question 2

How do you protect an Object from any modifications? No changes to values, no new/deleted properties?

Answer 2

Object.freeze(objectName)

Question 3

How do you protect an Object from new/deleted properties

Answer 3

Object.seal(objectName)

Question 4

How do you protect an Object from new properties only?

Answer 4

Object.preventExtensions(objectName)

Question 5

How do you compare the Objects properly?

Answer 5

1. JSON.stringify(object1) === JSON.stringify(object2)
2. _.isEqual(obj1, obj2)

Objects need to be converted to strings to be compared

Question 6

Iterating through an object dynamically

People often loop using for…in, but a better way is to get all Keys

Answer 6

console.log(Object.keys(product));
// ✅ [“name”, “specs”]

Question 7

Iterating through an object dynamically

People often loop using for…in, but a better way is to get all Values

Answer 7

console.log(Object.values(product));
// ✅ [“Laptop”, { ram: “16GB”, storage: “512GB” }]

Question 8

Iterating through an object dynamically

People often loop using for…in, but a better way is to get all Keys & Values

Answer 8

console.log(Object.entries(product));
// ✅ [[“name”, “Laptop”], [“specs”, { ram: “16GB”, storage: “512GB” }]]

Question 9

What does the for…of loop do in JavaScript?

Answer 9

It loops through the values of an array without needing an index.

let numbers = [10, 20, 30];
for (let num of numbers) {
console.log(num); // Prints 10, then 20, then 30
}

Question 10

What does break do inside a loop?

Answer 10

It stops the loop immediately when a condition is met.

for (let i = 0; i < 10; i++) {
if (i === 5) break; // Stops the loop when i is 5
console.log(i);
}

Question 11

Why use -Infinity when finding a maximum number?

Answer 11

-Infinity ensures any number is larger than it.

Question 12

What does && do inside an if statement?

Answer 12

It checks two conditions at the same time.

Question 13

Can multiple if statements run inside a function?

Answer 13

Yes! Unlike if-else, all if conditions will be checked.

Question 14

splice() heuristic for how each element works

Answer 14

arr.splice(index, howManyToRemove, valueToInsert)