Data Structure: Map in JavaScript

Overview

A map is an un ordered collection of key value pairs. Both keys and values can of any data type.

To retrieve a value, you can use the corssponding key.

Maps are iterables, They can be use of for…of loop.

Object Vs Map

Objects are unordered whereas maps are ordered.
Keys in object are strings or symbols, while keys in map can be of any data type.
An object has a prototype and may contain a few default keys which may collide with your keys if you’re not careful. A map on the other hand does not contain any keys by default.
Objects are not iterables where map are iterables.
The number of items in an object must be determined manually where it is readily available whith the size property in map.
Apart from storing data, you can attach functionality to an object whereas maps are restricted to storing data.

code example:

const map = new Map([
  ['a', 1],
  ['b', 2]
])

Here a and b are keys and 1 and 2 are values respectively. We can iterate using for of loop like this:

for (const [key, value] of map) {
  console.log(`${key}: ${value}`)
}

If we run the code we can see the values in console like this:

a: 1
b: 2

To add a key value in a map we use set method.

map.set('c', 3)

This is the method not a set datastructure. Please do not get confused.

If we run the code we see the three value.

To check if a key exists in a map we use has method.

console.log(map.has('a')) // true

If you want to delete a key value pair from a map we use delete method.

map.delete('a')

If we run the code we see the two value like this.

a: 1
b: 2

If you want to get the size of the map just use the size property.

console.log(map.size) // 2

To clear the map we use clear method.

console.log(map.clear())

And ther there is no any key value pair in the console.