Working with Maps

Question 1

What is a JavaScript Map?

Answer 1

A Map is a data structure that stores key-value pairs. Unlike objects, Maps allow keys to be any data type (objects, functions, primitives) and preserve insertion order.

Question 2

How do you create a new, empty JavaScript Map?

Answer 2

const myMap = new Map();

Question 3

How do you initialize a Map with initial key-value pairs when creating it?

Answer 3

const myArray = [[“name”, “John”], [“age”, 30]];
const myMap = new Map(myArray);

Question 4

How do you add a new key-value pair to a Map or update an existing value?

Answer 4

myMap.set(“city”, “New York”);
myMap.set(“age”, 31); // updates existing key

Question 5

How do you retrieve a value from a Map using its key?

Answer 5

const cityName = myMap.get(“city”); // ‘New York’
If key doesn’t exist, .get() returns undefined.

Question 6

How do you check if a Map contains a key?

Answer 6

myMap.has(“name”); // true
myMap.has(“address”); // false

Question 7

How do you remove a key-value pair from a Map?

Answer 7

myMap.delete(“city”); // true if removed, false otherwise

Question 8

How do you remove all key-value pairs from a Map?

Answer 8

myMap.clear(); // removes all entries

Question 9

How do you iterate through all key-value pairs in a Map?

Answer 9

for (const [key, value] of myMap) {
console.log(key, value);
}

Question 10

How do you iterate through all the keys in a Map?

Answer 10

for (const key of myMap.keys()) {
console.log(key);
}

Question 11

How do you iterate through all the values in a Map?

Answer 11

for (const value of myMap.values()) {
console.log(value);
}

Question 12

What is the significance of using objects as keys in a Map?

Answer 12

Maps allow associating data directly with objects — useful for caching or metadata storage.

Question 13

How do you get the number of key-value pairs in a Map?

Answer 13

const mapSize = myMap.size; // returns number of entries

Question 14

What are the key differences between Object and Map?

Answer 14

• Object keys must be strings/symbols; Map keys can be any type.
• Map preserves insertion order.
• Map has .size; Object requires manual counting.
• Map is directly iterable; Object needs Object.keys() or Object.entries().

Question 15

When might you choose Map over Object?

Answer 15

When you need:
- Non-string keys (objects/functions)
- Ordered entries
- Frequent add/remove operations
- Quick access to collection size (.size property)