Common methods of JS array

One 、 Array common methods

1.Array.isArray( Judgment content ) Determine whether it is an array , Returns... For the array true Do not return for array false

2. let arr2=Array.of( Parameters ） Definition arr2 An array of parameters

3.let arr=Array.from(obj) Replace the object with an array

( Generate a new array ）

4. Remove elements

arr.pop() Delete the last element of the array pop

arr.shift() Delete the first element of the array shift()

5. Additive elements  

    arr.push( Add content ) Add later push()

arr.unshift(1) Add unshift()

 6 Inversion array arr.reverse()

7.arr.splice() Delete , Add replacement array

2 Parameters     Delete

arr.splice( The starting position , Bottom position ）;

3 Parameters Add or replace

arr.splice( Starting position , length , Replace or add elements ）;

arr.splice(0,0,100);    Add... At the beginning 100

arr.splice(0,1,100);  Replace 0~1 That is, the first position element , Replace with 100

arr.splice(-1,0,500)  Add... At the penultimate position 500 Number of numbers

arr.splice(-1,1,600） Replace the last element with 600

 8.arr.sort() Scheduling problem   Default ascending sort , From small to large

（1） Array elements are numbers , Sort

arr.sort((a,b)=>a-b); Ascending From small to large

arr.sort((a,b)=>b-a); Descending From big to small

（2） Array elements are strings , Call directly arr.sort() Method

（3） Array objects

9.arr.copyWithin()  Copy and change the array

arr.copyWithin(index,start,end);

10.arr.fill(value,start,end) Fill change array

11. arr.slice(start,end)  Copy array elements

 12 arr.join() Convert an array to a string

13 arr.concat() Linked array

14 arr.toString() Array to string

15 arr.indexOf()  Query whether the element exists

arr.indexOf(" Query element ", Query start position ）; There is no return -1, There is a return subscript position

15 arr.lastIndexOf(value,index)  Reverse search

index Start looking for the penultimate

If there are multiple , Return the last element position , Otherwise, there is no return -1

 16 arr.includes(value,index) The result returns a Boolean value

  Two 、 Array traversal method

1.arr.forEach() Traversing elements

arr.forEach((value,index)=>{

console.log(' The value is '+value);

console.log(' Subscript to be '+index);

});

2.arr.some() Check whether the value in the array meets the condition , Having one can

// Check whether there is greater than 888 Value . If there is a return true, Otherwise return to false
arr.some(value=>value>888);

3.arr.every() Check whether all the conditions in the array are met

let arr=[1,2,3,4];
arr.every(value=>value>0) // return true, All conditions are met 
arr.every(value=>value>2) // return false, Only partially satisfied 

4.arr.filter(） Filter array   Return a new array

5.arr.map() Treat each element , Return a new array

 6.keys() Traverse the key name ,values() Traverse the key values , entries() Traversal key value pairs   

        arr=['a','b','c'];
        for(let i of arr.keys()){
            console.log(i)//keys() Ergodic subscript  0 1 2
        }
        for(let item of arr.values()){
            console.log(item)//values() Traversal value  a b c
        }
        for (let [i,item] of arr.entries()){
            console.log(i,item)//entries() Traverse subscripts and contents  
        }
    

 keys    values   entries

7.reduce() Accumulator of array , Merge into one value .
grammar arr.reduce((total, value, index, arr), init)

Parameters total( must )： Initial value , Then it is the return value of the previous callback .

 value( must ): The value of an array element .

 index( Optional ): Index value .

arr( Optional ): Array objects .

 init( Optional ): Initial value .

Return value ： The accumulated value

let arr = [1,2,3,4,5]
let sum = arr.reduce((total,value)=>total +value)
console.log(sum)//15
  

  Find out how many elements are in the array

 8.find() / findIndex() Find the array member by condition [ES6]
grammar arr.find(function(value, index, arr), this);

The parameter value is the same as froEach equally

Return value ： find() Return the first qualified array member , If there is no return undefined. findIndex() Return the index of the qualified array members .

let arr= [1,2,3,4,5]
let result = arr.find(item=>item>3)
console.log(result)//4  The first value is 
let result1 = arr.findIndex(item=>item>3)
console.log(result1)//3  The subscript of the first value 

9. arr.flat() Depth traversal expansion array

Array de reordering

let arr = [1,3,2,4,8,6,[5,1,3,5,9,10,5,[1,5,3,6,7,8,11,7,66]]]
let newarr = Array.from(new Set(arr.flat(Infinity))).sort((a,b)=>a-b)
console.log(newarr)//[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 66]

Array scrambling

var  arr  = [1,2,3,4,5,6,7,8,9]
 
for(let i =0;i<arr.length;i++){
    let sum = parseInt(Math.random()*(arr.length-1))
    let copyarr = arr[i];
         arr[i] = arr[sum]
         arr[sum] = copyarr
}
console.log(arr)

Refer to the post

It's all about carrying bloggers to learn , But taking notes is more familiar