Object Maps

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Object Maps

  • A Map stores key-value pairs, where the keys can be of any datatype.
  • A Map remembers the original insertion order of the keys.
  • A Map consists of 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 a new Map()
  • Create a Map and use Map.set()

new Map()

Create a Map by passing an Array to the new Map() constructor:

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Map Objects</h2>

<p>Creating a Map from an Array:</p>

<p id=”demo”></p>

<script>

// Create a Map

const fruits = new Map([

  [“apples”, 500],

  [“bananas”, 300],

  [“oranges”, 200]

]);

document.getElementById(“demo”).innerHTML = fruits.get(“apples”);

</script>

</body>

</html>

Output

JavaScript Map Objects

Creating a Map from an Array:

500

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

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Map Objects</h2>

<p>Using Map.set():</p>

<p id=”demo”></p>

<script>

// Create a Map

const fruits = new Map([

  [“apples”, 500],

  [“bananas”, 300],

  [“oranges”, 200]

]);

fruits.set(“apples”, 200);

document.getElementById(“demo”).innerHTML = fruits.get(“apples”);

</script>

</body>

</html>

Output

JavaScript Map Objects

Using Map.set():

200

Map.get()

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

Example

<!DOCTYPE html>

<html>

<body>

<h2>JavaScript Map Objects</h2>

<p>Using Map.get():</p>

<p id=”demo”></p>

<script>

// Create a Map

const fruits = new Map([

  [“apples”, 500],

  [“bananas”, 300],

  [“oranges”, 200]

]);

document.getElementById(“demo”).innerHTML = fruits.get(“apples”);

</script>

</body>

</html>

Output

JavaScript Map Objects

Using Map.get():

500


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