Set and map

Set And Map

Set

Definition

A set of unordered and non repetitive data sets

Methods and properties

1. （ One ） Method

• add()： to Set Set add data , Only one value can be added , It can be used continuously , Such as ：add(1).add(2)）
• has()： Judge Set Whether the collection has this value , There is a return true, No return false
• delete()： Delete Set Some data in the collection , You can only delete one value at a time . Delete nonexistent data , Nothing will happen , No errors reported
• clear()： Empty Set The data of
• forEach()： Traverse Set.s.forEach(function(value,key,set){},this Point to ),Set In the collection value and key Same value ,set This for traversal Set aggregate

2. （ Two ） attribute

• size：Set The length of the set , It's equivalent to length

Set Arguments to the constructor

• Array
• character string
• arguments
• NodeList
• Set

// Copy a Set,s2 It's not equal to s1
const s1 = new Set([1,2,3]);
const s2 = new Set(s1);

Be careful ：Set Judge whether the data is repeated according to === principle , but NaN Different ,Set Medium NaN be equal to NaN

Map

Definition

Set of key value pairs ,Map Any data type can be used as its key, Arrays can only be legal identifiers

Methods and properties

1. （ One ） Method

• set()： Add a new key value pair , If the key already exists , The key value pair added after overwriting the existing
• get()： Get value by key
• has()： Judge Map Is there a key in the
• delete()： Delete a data , If you delete a key that does not exist , Nothing will happen and no error will be reported
• clear()： Delete all data
• forEach()： Traverse Map,m.forEach(function(value,key,map){},this Point to )

2. （ Two ） attribute

• size：Map The length of , Similar to... In an array length

Map Arguments to the constructor

• Array （ It can only be a two-dimensional array ）

const map = new Map([
	['name': 'xxx'],
	['age': 18]
])

• Set（ In the form of a two-dimensional array ）、Map

// Copy Map
const m1 = new Map([
	['name': 'xxx'],
	['age': 18]
])
const m2 = new Map(m1)

Be careful ：Map Of NaN And Set equally , The same is true for key names