Common methods of arrays in JavaScript

1,push()

add new content to the end of the array

Parameters: The item to add. Pass multiple separated by commas, any data type is fine

Return value: the length of the added array

Whether to change the original array: change

let ary1 = [12,34,26];
ary1.push(100); //returns a new length 
length=4console.log(ary1)//The result is [12,34,26,100]

2,pop()

delete the last item of an array

Parameters: none

Return value: deleted item

Whether to change the original array: change

let ary2 = [108,112,39,10];
ary2.pop();//The last item removed is 10
console.log(ary2);//[108, 112, 39]

3,shift()

delete the first item of the array

Parameters: none

Return value: deleted item

Whether to change the original array: change

let ary3 = [0,108,112,39];
ary3.shift();//The first item removed is 0
console.log(ary3);//[108, 112, 39]

4,unshift()

Add new content to the first of the array

Parameter: item to be added, multiple items are separated by ','

Return value: the length of the new array

Whether to change the original array: change

let ary4 = ['c','d'];
ary4.unshift('a','b');
console.log(ary4);//["a", "b", "c", "d"]

5,slice()

Find some of them by condition

parameter:

array.slice(n, m), starting from index n to m (excluding m)
array.slice(n) If the second parameter is omitted, it will search until the end
array.slice(0) outputs the content as it is, which can realize array cloning
array.slice(-n,-m) slice supports negative parameters, starting from the last item, -1 is the last item, -2 is the penultimate item

Return value: returns a new array

Whether to change the original array: no change

let ary5 = [1,2,3,4,5,6,7,8,9]; 
//console.log(ary5.slice(2,8));//Start from index 2 to find the content with index 8, the result is [3, 4, 5, 6, 7, 8] 
//console.log(ary5.slice(0)); 
console.log(ary5.slice(-2,-1));//[8]

6,splice()

Add, delete and modify the array

Addition: ary.splice(n,0,m) deletes 0 items from index n, and inserts m or more contents before index n

return empty array

Modification: ary.splice(n,x,m) deletes x from index n, and m replaces the deleted part

Delete the original content and replace it with the new content

Delete: ary.splice(n,m) delete m contents from index n

(If the second parameter is omitted, it is removed from n to the end)

Returns the deleted new array, the original array changed

//Increase
  let ary6_z = [33,44,55,66,77,88];
  ary6_z.splice(2,0,'a','b')
  console.log(ary6_z);// [33, 44, "a", "b", 55, 66, 77, 88]

  //Revise
  let ary6_x = [33,44,55,66,77,88];
  ary6_x.splice(1,2,'x','y')
  console.log(ary6_x);// [33, "x", "y", 66, 77, 88]

  //delete
   let ary6_s = [33,44,55,66,77,88];
   //console.log(ary6.splice(3,2))//[66, 77]
   console.log(ary6_s.splice(3));//[66, 77, 88]

7,join()

Concatenates each item of the array into a string with the specified delimiter

Parameter: the specified delimiter (if the parameter is omitted, a comma is used as the delimiter)

Return value: concatenated string

Whether to change the original array: no change

let ary7 = [1,2,3];
console.log(ary7.join(','));//1,2,3

8,concat()

for concatenating two or more arrays

Parameters: Parameters can be concrete values ​​or array objects. can be any number of

Return value: Returns the new array after concatenation

Whether to change the original array: no change

let ary8 = ['you'];
let ary80 = ary8.concat('it is good');
console.log(ary80);//["Hello"]

9,indexOf()

Detects the position index of the first occurrence of the current value in an array

Parameters: array.indexOf(item,start) item: the element to be searched start: the position in the string to start the search

Return value: the index found for the first time, if not found, return -1

Whether to change the original array: no change

let ary9 = ['a','b','c','d','e','a','f'];   
console.log(ary9.indexOf('c'));//2
console.log(ary9.indexOf('a',3))//5

10,lastIndexOf()

Detects the position index of the last occurrence of the current value in an array

Parameters: array.lastIndexOf(item,start) item: the element to be searched start: the position in the string to start the search

Return value: the index found for the first time, if not found, return -1

Whether to change the original array: no change

let ary10 = ['a','b','c','d','e','a','f'];   
console.log(ary10.lastIndexOf('c'));//2
console.log(ary10.lastIndexOf('f',1))//-1

11,includes()

Checks if an array contains a specified value

Parameters: the specified content

Return value: boolean

Whether to change the original array: no change

let ary13 = ['a','b','c','d']; 
console.log(ary13.includes('c'));//true
console.log(ary13.includes(2));//false

12,sort()

Sort the elements of the array (the default is to sort from small to large and according to the string)

Arguments: optional (function) Specifies the collation. The default sort order is ascending alphabetical order

Return value: new array after sorting

Whether to change the original array: change

sort can only process numbers within 10 (single digits) without passing parameters

let ary11 = [32,44,23,54,90,12,9]; 
  ary11.sort(function(a,b){        // return a-b; // result [9, 12, 23, 32, 44, 54, 90]
       // return b-a; // result [90, 54, 44, 32, 23, 12, 9] })  
   console.log(ary11);

13,reverse()

reverse the array

Parameters: none

Return value: new array in reverse order

Whether to change the original array: change

let ary12 = [6,8,10,12]; 
console.log(ary12.reverse());//[12, 10, 8, 6]

14,forEach()

Loop through each item in the array

Parameters: function ary.forEach(function(item,index,ary){}) item: each item index: index ary: current array

Return value: none

Whether to change the original array: no change

You cannot use continue and break in forEach, you cannot jump out in forEach, you can only skip (return skip)

let ary14 = ['a','b','c','d']; 
let item = ary14.forEach(function(item,index,ary){
       console.log(item,index,ary);
  })