What are the commonly used methods for arrays?

Commonly used methods in arrays are: 1. The push method to add new content to the end of the array; 2. The pop method to delete the last item of the array; 3. The shift method to delete the first item of the array; 4. Add new content to the first part of the array using the unshift method and so on.

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Some commonly used arrays Method:

1. push()

Add new content to the end of the array

Parameters: The item to be added. Pass multiple numbers separated by commas. Any data type is acceptable.

Return value: The length of the new array.

Whether to change the original array: Change

let ary1 = [12,34,26];
ary1.push(100); //返回一个新的长度 
length=4console.log(ary1)//结果为 [12,34,26,100]

2. pop()

Delete the last item of the array

Parameters: None

Return value: Whether the deleted item

has changed Original array: change

let ary2 = [108,112,39,10];
ary2.pop();//删除的最后一项为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();//删除的第一项为0
console.log(ary3);//[108, 112, 39]

4. unshift()

Add new content to the first part of the array

Parameters: items to be added, multiple items separated by ','

Return value: length of 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 part of the content according to the conditions

Parameters:

array.slice(n, m), from Search from index n to m (excluding m)

array.slice(n) If the second parameter is omitted, search until the end

array.slice(0) and output the content as is , array cloning can be realized

array.slice(-n,-m) slice supports negative parameters, counting from the last item, -1 is the last item, and -2 is the penultimate item

Return value: Return a new array

Whether to change the original array: Do not change

let ary5 = [1,2,3,4,5,6,7,8,9]; 
//console.log(ary5.slice(2,8));//从索引2开始查找到索引为8的内容，结果为[3, 4, 5, 6, 7, 8] 
//console.log(ary5.slice(0)); 
console.log(ary5.slice(-2,-1));//[8]

6, splice()

to the array Add, delete, modify

Add: ary.splice(n,0,m) deletes 0 items starting from index n, and inserts m or more content in front of index n

Returns empty Array

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

Delete the original content, and then replace it with the new content

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

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

Return the deleted new array, the original array changes

//增加
  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]

  //修改
  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]

  //删除
   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()

Use the specified delimiter to splice each item of the array into a string

Parameter: Specified delimiter (if this parameter is omitted, comma is used as the delimiter)

Return value: The spliced ​​string

Whether the original array is changed: Do not change

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

8, concat()

Used to connect two or more arrays

Parameters: Parameters can be specific values, It can also be an array object. It can be any number of

Return value: Return the new array after connection

Whether to change the original array: No change

let ary8 = ['你'];
let ary80 = ary8.concat('好');
console.log(ary80);//["你", "好"]

9, indexOf()

Detect the index of the first occurrence of the current value in the array

Parameters: array.indexOf(item,start) item: the element being searched for start: the position in the string where the search begins

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()

Detect the position index of the last occurrence of the current value in the array

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

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( )

Judge whether an array contains a specified value

Parameter: Specified content

Return value: Boolean value

Whether the original value is changed Array: Do not 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 based on strings) )

Parameter: Optional (function) Specifies the sorting rule and the default sort order is in 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;  // 结果[9, 12, 23, 32, 44, 54, 90]
        // return b-a;  // 结果[90, 54, 44, 32, 23, 12, 9]   })  
    console.log(ary11);

13, reverse()

Array the array upside down

Parameters: None

Return value: New array after 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 of 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

continue and break cannot be used in forEach, and cannot jump out in forEach, only skip (return skip)

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

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