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JavaScript Map Objects

A Map object holds key-value pairs where the keys can be any datatype.

A Map object remembers the original insertion order of the keys.

A Map object has a property that represents the size of the map.

Essensial Map() Methods

MethodDescription
new Map()Creates a new Map object
set()Sets a value for a key in a Map object
get()Gets a value for a key in a Map object
entries()Returns an array of the key/value pairs in a Map object
keys()Returns an array of the keys in a Map object
values()Returns an array of the values in a Map object

Map() Properties

PropertyDescription
sizeGets a value for a key in a Map object

Create a Map Object

Being able to use an Object as a key is an important Map feature.

Example

// Create Objects
const apples = {name: 'Apples'};
const bananas = {name: 'Bananas'};
const oranges = {name: 'Oranges'};

// Create a new Map
const fruits = new Map();

// Add new Elements to the Map
fruits.set(apples, 500);
fruits.set(bananas, 300);
fruits.set(oranges, 200);
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The get() method gets a value for a key in a Map object:

Example

fruits.get(apples);    // Returns 500
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fruits.get("apples");  // Returns undefined
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You can pass an Array to the new Map() constructor:

Example

// Create Objects
const apples = {name: 'Apples'};
const bananas = {name: 'Bananas'};
const oranges = {name: 'Oranges'};

// Create a new Map
const fruits = new Map([;
  [apples, 500],
  [bananas, 300],
  [oranges, 200]
]);
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Other Map() Methods

MethodDescription
clear()Removes all elements in a Map
delete()Removes an element specified by a key.
has()Returns true if a key exists.
forEach()Invokes a callback for each key/value pair.