1: Map method
/ * = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Map method = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = * / / / / / class object and object is the difference between: Object's key must be a string, Map keys to say any type let arr1 = [[' name ', 'li bai'], [' professional ', 'poets'], [false,' is a Boolean value], [[], 'is an array of']] let m = new Map (arr1). / / the console log (m) / / Map {' name '= >' li ', 'professional' = > 'poets' false = >' is a Boolean value, [] => 'array'} for (let [key,value] of m) {// console.log(' key: ',key) // console.log(' value: ',value)}Copy the code
Note:
- Map method:
map.has(keyStr)
Is used to determine whether attributes exist in the mapkeyStr
, the return value is a Booleanmap.set(keyStr,itemVal)
.keyStr
Is a property,itemVal
Is the value, theitemVal
Save to mapmap.delete('keyStr')
, delete thekey
forkeyStr
The data ofmap.get('keyStr')
To obtainkey
forkeyStr
The data ofmap.values()
To obtainmap
Worth set, pass[...map.values()]
A collection of values is returned to an array
- Differences between a Map and a common object
Map
Properties can be arbitrary values, and ordinary objects can only be stringsMap
To distinguish the characters'a'
And lettersa
, ordinary objects do not distinguish, the following value will overwrite the previous value
Such as:
/ / common object obj = {a: 'I am a letter a', 'a' : 'I am a string of 1:' ordinary employees, 2: 'boss', 1: 'administrators',' 2 ', 'VIP customers'} the console. The log (obj) / / {1: "Admin ",2: "VIP customer ", A:" I am string A "}Copy the code
Map.set (a,' I am the letter A ')
Error will be reported, need to changeMap.set ('a',' I am string a')
Two: Set() method
/ * = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Set method = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = * / / / / / class array and array is the difference between: Array is [] surrounded, Set is {} surrounded, Let s = new Set(arr2) // console.log(s) // Set {1,2,3, 4, 4, 5} // instance 1: Let temp21 = [1,2,4,2,3,1,5] let temp22 = [1,4,4,2,10,1,9 Set(temp21) let tempArr22 = new Set(temp22) return Array.from(tempArr21).filter(item => { return tempArr22.has(item) }) } // Example 2: Function unBothHas(temp21,temp22) {let tempArr21 = new Set(temp21) let tempArr22 = new Set(temp22) return function unBothHas(temp21,temp22) {let tempArr21 = new Set(temp22) return Array.from(tempArr21).filter(item => { return ! tempArr22.has(item) }) } console.log('data2==',bothHas(temp21,temp22)) console.log('data3==',unBothHas(temp21,temp22))Copy the code
Note:
- The Set method:
set.add(val)
To add valueset.delete(val)
, delete the valueset.has(val)
, determine if there isval
value
- Set attributes:
set.size
Returns the number of elements contained in the collection