JavaScript Map

A Map is an object in JavaScript that stores entries of key-value pairs in their original insertion order.

• Values mapped to existing keys can be overwritten later.
• Keys/values can either be an object or a variable of any data type.
• Maps are directly iterable whereas objects are not.

Syntax

A map can be defined with the new keyword. The example below creates an empty Map object, map:

const map = new Map();

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Example

To create a non-empty Map object, an array of arrays is passed into Map(). Each inner array represents a key-value pair:

const hogwartsStudents = new Map([
  ['Gryffindor', 'Harry Potter'],
  ['Slytherin', 'Draco Malfoy'],
  ['Hufflepuff', 'Cedric Diggory'],
]);

console.log(hogwartsStudents);

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The output will be:

Map(3) {
  'Gryffindor' => 'Harry Potter',
  'Slytherin' => 'Draco Malfoy',
  'Hufflepuff' => 'Cedric Diggory'
}

Codebyte Example

In the example below, an addressBook maps a person’s name to a phone number. By the end of the program:

• Tom has moved and deleted their phone number with the .delete() method.
• Paul has changed their phone number using the .set() method.

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