Creating map in javascript

JavaScript Maps

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

A Map remembers the original insertion order of the keys.

Essential Map Methods

Method	Description
new Map()	Creates a new Map
set()	Sets the value for a key in a Map
get()	Gets the value for a key in a Map
delete()	Removes a Map element specified by the key
has()	Returns true if a key exists in a Map
forEach()	Calls a function for each key/value pair in a Map
entries()	Returns an iterator with the Creating map in javascript pairs in a Map
Property	Description
size	Returns the number of elements in a Map

How to Create a Map

You can create a JavaScript Map by:

The new Map() Method

You can create a Map by passing an Array to the new Map() constructor:

Example

The set() Method

You can add elements to a Map with the set() method:

Example

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

// Set Map Values
fruits.set(«apples», 500);
fruits.set(«bananas», 300);
fruits.set(«oranges», 200);

The set() method can also be used to change existing Map values:

Example

The get() Method

The get() method gets the value of a key in a Map:

Example

The size Property

The size property returns the number of elements in a Map:

Example

The delete() Method

The delete() method removes a Map element:

Example

The has() Method

The has() method returns true if a key exists in a Map:

Example

Try This:

JavaScript Objects vs Maps

Differences between JavaScript Objects and Maps:

Object	Map
Iterable	Not directly iterable	Directly iterable
Size	Do not have a size property	Have a size property
Key Types	Keys must be Strings (or Symbols)	Keys can be any datatype
Key Order	Keys are not well ordered	Keys are ordered by insertion
Defaults	Have default keys	Do not have default keys

The forEach() Method

The forEach() method calls a function for each key/value pair in a Map:

Example

// List all entries
let text = «»;
fruits.forEach (function(value, key) text += key + ‘ = ‘ + value;
>)

The entries() Method

The entries() method returns an iterator object with the Creating map in javascript in a Map:

Example

Browser Support

JavaScript Maps are supported in all browsers, except Internet Explorer:

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Map() constructor

The Map() constructor creates Map objects.

Syntax

Note: Map() can only be constructed with new . Attempting to call it without new throws a TypeError .

Parameters

An Array or other iterable object whose elements are key-value pairs. (For example, arrays with two elements, such as [[ 1, ‘one’ ],[ 2, ‘two’ ]] .) Each key-value pair is added to the new Map .

Examples

Creating a new Map

const myMap = new Map([ [1, "one"], [2, "two"], [3, "three"], ]); 

Specifications

Browser compatibility

BCD tables only load in the browser

See also

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JavaScript Maps

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

A Map remembers the original insertion order of the keys.

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

Map Methods

Method	Description
new Map()	Creates a new Map object
set()	Sets the value for a key in a Map
get()	Gets the value for a key in a Map
clear()	Removes all the elements from a Map
delete()	Removes a Map element specified by a key
has()	Returns true if a key exists in a Map
forEach()	Invokes a callback for each key/value pair in a Map
entries()	Returns an iterator object with the Creating map in javascript pairs in a Map
keys()	Returns an iterator object with the keys in a Map
values()	Returns an iterator object of the values in a Map

Property	Description
size	Returns the number of Map elements

How to Create a Map

You can create a JavaScript Map by:

new Map()

You can create a Map by passing an Array to the new Map() constructor:

Example

Map.set()

You can add elements to a Map with the set() method:

Example

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

// Set Map Values
fruits.set(«apples», 500);
fruits.set(«bananas», 300);
fruits.set(«oranges», 200);

The set() method can also be used to change existing Map values:

Example

Map.get()

The get() method gets the value of a key in a Map:

Example

Map.size

The size property returns the number of elements in a Map:

Example

Map.delete()

The delete() method removes a Map element:

Example

Map.clear()

The clear() method removes all the elements from a Map:

Example

Map.has()

The has() method returns true if a key exists in a Map:

Example

Try This:

Maps are Objects

Example

instanceof Map returns true:

Example

JavaScript Objects vs Maps

Differences between JavaScript Objects and Maps:

Object	Map
Not directly iterable	Directly iterable
Do not have a size property	Have a size property
Keys must be Strings (or Symbols)	Keys can be any datatype
Keys are not well ordered	Keys are ordered by insertion
Have default keys	Do not have default keys

Map.forEach()

The forEach() method invokes a callback for each key/value pair in a Map:

Example

// List all entries
let text = «»;
fruits.forEach (function(value, key) text += key + ‘ = ‘ + value;
>)

Map.entries()

The entries() method returns an iterator object with the Creating map in javascript in a Map:

Example

Map.keys()

The keys() method returns an iterator object with the keys in a Map:

Example

Map.values()

The values() method returns an iterator object with the values in a Map:

Example

You can use the values() method to sum the values in a Map:

Example

Objects as Keys

Being able to use objects as keys is an important Map feature.

Example

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

// Add new Elements to the Map
fruits.set(apples, 500);
fruits.set(bananas, 300);
fruits.set(oranges, 200);

Remember: The key is an object (apples), not a string («apples»):

Example

Browser Support

JavaScript Maps are supported in all browsers, except Internet Explorer:

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