Map in JavaScript

In JavaScript, a Map is a built-in object that allows you to store key-value pairs, similar to an object. However, a Map offers some additional functionality that makes it useful in certain situations.

Here’s an example of creating a Map:

const myMap = new Map();

To add a key-value pair to the Map, you can use the set() method:

myMap.set('key1', 'value1');
myMap.set('key2', 'value2');

You can retrieve a value from the Map using the get() method:

console.log(myMap.get('key1')); // output: 'value1'

You can also check if a key exists in the Map using the has() method:

console.log(myMap.has('key1')); // output: true
console.log(myMap.has('key3')); // output: false

To remove a key-value pair from the Map, you can use the delete() method:

myMap.delete('key2');

You can iterate over the keys or values in a Map using a for…of loop:

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

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

Additionally, you can iterate over both keys and values using the entries() method:

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

One useful feature of a Map is that you can use objects as keys, rather than just strings or numbers:

const obj1 = {name: 'John'};
const obj2 = {name: 'Jane'};

const myMap = new Map();
myMap.set(obj1, {age:  15});
myMap.set(obj2, {age:  20});

console.log(myMap.get(obj1)); // output: 'value1'

Another advantage of using a Map is that you can easily get the size of the Map using the size property:

console.log(myMap.size); // output: 2

In summary, a Map is a built-in object in JavaScript that allows you to store key-value pairs, with additional functionality for checking key existence, iterating over keys and values, and using objects as keys.

For more information, refer: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map