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JavaScript Map() Constructor - GeeksforGeeks

Last Updated : 23 Jul, 2025

The Map() constructor is used to create Map objects in JavaScript. The map is a data structure that stores elements as a key, value pair.

new Map()
new Map(iterable)

• iterable: An iterable object used for iterating through elements, stored as a key, value pair.

• A new Map object returns after the initialization of the map constructor.  

Example 1:

// map1 contains 
// 1 => 10
// 2 => 20
// 3 => 30
// 4 => 40
let map1 = new Map([
    [1, 10], [2, 20],
    [3, 30], [4, 40]
]);

console.log("Map1: ");
console.log(map1);

Output:

Map1: 
Map(4) { 1 => 10, 2 => 20, 3 => 30, 4 => 40 }

Example 2:

// map2 contains 
// firstname => Ram
// lastname => Prasad
// website => geeksforgeeks 
let map2 = new Map([
    ["firstname", "Ram"],
    ["lastname", "Prasad"],
    ["website", "geeksforgeeks"]
]);

console.log("Map2: ");
console.log(map2);

Output:

Map2:
Map(3) {
 'firstname' => 'Ram',
 'lastname' => 'Prasad',
 'website' => 'geeksforgeeks'
}

Example 3:

// Map contains nested array
let map3 = new Map([
    ["whole numbers", [1, 2, 3, 4]],
    ["Decimal numbers", [1.1, 1.2, 1.3, 1.4]],
    ["negative numbers", [-1, -2, -3, -4]]
]);

console.log("Map3: ");
console.log(map3);

Output:

Map3:
Map(3) {
 'whole numbers' => [ 1, 2, 3, 4],
 'Decimal numbers' => [ 1.1, 1.2, 1.3, 1.4],
 'negative numbers' => [ -1, -2, -3, -4]
}

• Chrome 38
• Edge 12
• Firefox 13
• Opera 25
• Safari 8

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