FilesExpand file tree

 master

/

map-set-get.js

Copy path

Blame

More file actions

Blame

More file actions

Latest commit

 

History

History

History

51 lines (35 loc) · 1.58 KB

 master

/

map-set-get.js

Copy path

Top

File metadata and controls

• Code
• Blame

51 lines (35 loc) · 1.58 KB

Raw

Copy raw file

Download raw file

Open symbols panel

Edit and raw actions

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

/*

Objects for storing keyed collections.

Arrays for storing ordered collections.

But that’s not enough for real life. That’s why Map and Set also exist.

Map

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

The main methods 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() – clears the map

map.size – returns the current element count. */

// EXAMPLE-1

let map = new Map(),

val2 = 'val2',

val3 = {

key: 'value'

};

console.log(map) // => Map {}

map.set(0, 'val-1')

console.log(map) // => Map { 0 => 'val-1' }

// EXAMPLE-2 Map can also use objects as keys

let john = { name: "John" };

// for every user, let's store his visits count

let visitsCountMap = new Map();

// john is the key for the map

visitsCountMap.set(john, 123);

// console.log(visitsCountMap.get(john) ); // 123

console.log(visitsCountMap) // => Map { { name: 'John' } => 123 }

/* Using objects as keys is one of most notable and important Map features. For string keys, Object can be fine, but it would be difficult to replace the Map with a regular Object in the example above. In the old times, before Map existed, people added unique identifiers to objects for that like below */

let john_old = { name: 'john-old', id : 1}

let visitsCounts = {}

visitsCounts[john.id] = 123;