Some methods of operating arrays in js

define an array

var numbers= ['1','2','3','4','5'];

1. Delete the tail element

this.numbers.pop();

2. Add elements at the end

this.numbers.push('6');

3. Delete the first element

this.numbers.shift();

4. Add elements to the header

this.numbers.unshift('0');

5. The first parameter is the starting position, and the second parameter is the number of deletions.

 this.numbers.splice(1,3);

6. Sorting

this.numbers.sort();

7. Reversal

this.numbers.reverse();

8. Filter

let result = numbers.filter(function (number){
    
    
          return number > 4
        });

9. Multiply each piece of data by 2

let result2 = numbers.map(function (number){
    
    
          return number * 2;
        });

10. Summation

let total = numbers.reduce(function (preValue,value){
    
    
          return preValue + value;
        },0);

Parameter 1: Callback function. This function has two parameters. Parameter 1 is the value returned by this method in the last loop. Parameter 2 is the element of the current loop. Parameter 2: The
default value of the first parameter of the callback function when called for the first time.
return preValue + value; Function: Add all the values ​​in the array and return a number