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JavaScript Map() Constructor

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  • Last Updated : 20 May, 2021
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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.

Syntax:

new Map()
new Map(iterable)

Parameters:

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

Return value: A new Map object returns after the initialization of the map constructor.

 

Example 1:

Javascript




<script>
  
// map1 contains 
// 1 => 10
// 2 => 20
// 3 => 30
// 4 => 40
var map1 = new Map([
    [1 , 10], [2 , 20] ,
    [3, 30],[4, 40]
]);
  
console.log("Map1: ");
console.log(map1);
</script>

Output:

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

Example 2:

Javascript




<script>
  
// map2 contains 
// firstname => Ram
// lastname => Prasad
// website => geeksforgeeks 
var map2 = new Map([
    ["firstname" ,"Ram"], 
    ["lastname", "Prasad"], 
    ["website", "geeksforgeeks"]
]);
    
console.log("Map2: ");
console.log(map2);
</script>

Output:

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

Example 3:

Javascript




<script>
  
// Map contains nested array
var 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);
</script>

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]
}

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