JavaScript Map Object

The JavaScript Map object is used to map keys to values. It stores each element as key-value pair. It operates the elements such as search, update and delete on the basis of specified key.

Parameter

iterable - It represents an array and other iterable object whose elements are in the form of key-value pair.

Points to remember

• A map object cannot contain the duplicate keys.
• A map object can contain the duplicate values.
• The key and value can be of any type (allows both object and primitive values).
• A map object iterates its elements in insertion order.

Map is a collection of keyed data items, just like an Object. But the main difference is that Map allows keys of any type.

Methods and properties are:

• new Map() – creates the map.
• map.set(key, value) – stores the value by the key.
• map.get(key) – returns the value by the key, undefined if key doesn’t exist in map.
• map.has(key) – returns true if the key exists, false otherwise.
• map.delete(key) – removes the value by the key.
• map.clear() – removes everything from the map.
• map.size – returns the current element count.

For instance:

let map = new Map();

map.set('1', 'str1');   // a string key
map.set(1, 'num1');     // a numeric key
map.set(true, 'bool1'); // a boolean key

// remember the regular Object? it would convert keys to string
// Map keeps the type, so these two are different:
alert( map.get(1)   ); // 'num1'
alert( map.get('1') ); // 'str1'

alert( map.size ); // 3