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 [key, value] 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:

• Passing an Array to new Map()
• Create a Map and use Map.set()

new Map()

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

Example

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

-

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

fruits.set("apples", 500);

-

Map.get()

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

Example

fruits.get("apples");    // Returns 500

-

Map.size

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

Example

fruits.size;

-

Map.delete()

The delete() method removes a Map element:

Example

fruits.delete("apples");

-

Map.clear()

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

Example

fruits.clear();

-

Map.has()

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

Example

fruits.has("apples");

-

Try This:

fruits.delete("apples");
fruits.has("apples");

-

Maps are Objects

typeof returns object:

Example

// Returns object:
typeof fruits;

-

instanceof Map returns true:

Example

// Returns true:
fruits instanceof Map;

-

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 [key,values] in a Map:

Example

// List all entries