JavaScript – Create a Map

To create a Map in JavaScript, use Map() constructor. Map() constructor accepts an array of arrays, where inner array contains key and value as elements.

Syntax

The syntax to create a Map using Map() constructor is

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new Map() //empty map
new Map([[key, value], [key, value]]) //map from array

Examples

In the following example, we create an empty map, and insert some key-value pairs into it.

index.html

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<!DOCTYPE html>
<html lang="en">
<body>
    <pre id="output"></pre>
    <script>
        var map1 = new Map();
        map1.set('a', 10);
        map1.set('b', 20);

        var displayOutput = '';
        map1.forEach (function(value, key) {
            displayOutput += key + ' - ' + value + '\n';
        });
        document.getElementById('output').innerHTML += displayOutput;
    </script>
</body>
</html>

In the following example, we create a map with key-value pairs derived from an array of arrays passed as argument to Map() constructor.

index.html

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<!DOCTYPE html>
<html lang="en">
<body>
    <pre id="output"></pre>
    <script>
        var map1 = new Map([
            ['a', 10],
            ['b', 20],
            ['c', 30]
        ]);

        var displayOutput = '';
        map1.forEach (function(value, key) {
            displayOutput += key + ' - ' + value + '\n';
        });
        document.getElementById('output').innerHTML += displayOutput;
    </script>
</body>
</html>

Conclusion

In this JavaScript Tutorial, we learned how to create a Map in JavaScript using Map() constructor, with examples.