Modifier prevention: changes the value of the object calling them

1. copyWithin(), inside the array, copy a sequence of elements to another sequence of elements, and overwrite the original value

Usage -- copyWithin(target,start,end)

Parameters: target -- copy where to start insertion start -- copy where to start the element end -- copy where to end the element

var arr1 = [1, 2, 3, 4, 5, 6, 7, 8];
arr1.copyWithin(3, 4, 5);

console.log(arr1);          //[ 1, 2, 3, 5, 5, 6, 7, 8 ]
console.log(arr1);          //[ 1, 2, 3, 5, 5, 6, 7, 8 ]

2. fill(), fill all elements in an array from the start index to the end index with a fixed value. Exclude termination index

Usage: array.fill(value,star,end)

Parameter: Value -- replacement value start -- start position, default is 0 end -- end position, default is array.length

var arr1 = [4, 6, 9, 2, 43, 5, 1];
var arr2 = [4, 6, 9, 2, 43, 5, 1];

arr1.fill('a', 0, 3);
arr2.fill('b');

console.log(arr1);              //[ 'a', 'a', 'a', 2, 43, 5, 1 ]
console.log(arr2);              //[ 'b', 'b', 'b', 'b', 'b', 'b', 'b' ]

3. pop(), delete the last element of the array

var arr = [5, 2, 7, 9, 3];

console.log(arr.pop());         //3
console.log(arr);               //[ 5, 2, 7, 9 ]

4.push() adds one or more elements to the array by default, and returns the length of the new array

var arr = [3, 6, 9, 2, 4];

console.log(arr.push('h', 'i'));            //7
console.log(arr);                           //[ 3, 6, 9, 2, 4, 'h', 'i' ]

5. reverse(), reverse the order of elements

var arr = [6, 3, 8, 9];

console.log(arr.reverse());             //[ 9, 8, 3, 6 ]
console.log(arr);                       //[ 9, 8, 3, 6 ]

6. shift(), delete the first element of the array

var arr = [6, 3, 2, 6, 8, 5];

console.log(arr.shift());           //6
console.log(arr);                   //[ 3, 2, 6, 8, 5 ]

7. sort() to sort the array

var arr1 = ['c','a','d','b'];
var arr2 = [4,7,1,9,12,0];

console.log(arr1.sort());                           //[ 'a', 'b', 'c', 'd' ]
console.log(arr1);                                  //[ 'a', 'b', 'c', 'd' ]            
console.log(arr2.sort(function(a,b){return a-b}));  //[ 0, 1, 4, 7, 9, 12 ]
console.log(arr2);                                  //[ 0, 1, 4, 7, 9, 12 ]  

8. splice(), add or delete any element to the array at any position

Usage: splice(index,howmany,item,...item)

Parameter: index - required, where the element starts to modify howmany - required, number of elements deleted item...item - optional, new element

var arr1 = [3,7,9,14];
var arr2 = [3,7,9,14];
var arr3 = [3,7,9,14];

console.log(arr1.splice(1,0,'a','b'));          //[]
console.log(arr1);                              //[ 3, 'a', 'b', 7, 9, 14 ]
console.log(arr2.splice(0,2,'hi'));             //[ 3, 7 ]
console.log(arr2);                              //[ 'hi', 9, 14 ]
console.log(arr3.splice(0,1));                  //[3]
console.log(arr3);                              //[ 7, 9, 14 ]

9. unshift(), add one or more elements at the beginning of the array, and return the array length

var arr = [4,7,2,6,8,2];

console.log(arr.unshift(0,1,4));            //9
console.log(arr);                           //[ 0, 1, 4, 4, 7, 2, 6, 8, 2 ]