JavaScript - Map Methods Part 1: Basic Map Creation and Properties

1. Creating a Map

A Map is created using the new Map() constructor. It can either start empty or be initialized with key-value pairs.

Example 1: Empty Map

const myMap = new Map();

console.log(myMap); // Map(0) {}

Example 2: Pre-filled Map

const cities = new Map([

  ["New York", "USA"],

  ["Paris", "France"],

  ["Tokyo", "Japan"],

]);

console.log(cities); 

// Output: Map(3) { 'New York' => 'USA', 'Paris' => 'France', 'Tokyo' => 'Japan' }

2. Properties of a Map

size Property

The size property returns the number of key-value pairs in the Map.

Example:

console.log(cities.size); // 3

Maps maintain the insertion order of their keys, unlike plain objects.

Example:

cities.set("Berlin", "Germany");

console.log([...cities.keys()]); // ['New York', 'Paris', 'Tokyo', 'Berlin']