Learning JavaScript Arrays

1 Creation of arrays

 var arr1 = new Array();
 var arr2=[1,2,3];

2 Commonly used methods for arrays:

push, pop, shift, unshift, splice, slice, sort, reverse

2.1 push method: insert elements at the end of the element

var arr=[1,2,3];
var result = arr.push(1,3,4);//返回新数组的长度
console.log("arr:"+arr);
console.log("result:"+result);

Result:

arr:1,2,3,1,3,4
result:6

2.2 pop method: Pop an element at the end of the element

var arr=[1,2,3];
var result = arr.pop();//返回弹出元素的值
console.log("arr:"+arr);
console.log("result:"+result);

Result:

arr:1,2
result:3

2.3 shift method: pop up an element at the beginning of the element

var arr=[1,2,3];
var result = arr.shift();//返回弹出元素的值
console.log("arr:"+arr);
console.log("result:"+result);

result:

arr:2,3
result:1

2.4 unshift method: insert an element at the beginning of the element

var arr=[1,2,3];
var result = arr.unshift(4,5);//返回新数组的长度
console.log("arr:"+arr);
console.log("result:"+result);

result:

arr :4,5,1,2,3
result:5

2.5 splice method: intercept the array, then insert the data, directly operate the array itself

var arr=[1,2,3,4,5];
arr.splice(1,2,3,4);
console.log("arr:"+arr);

Result:

arr:1,3,4,4 ,5

Analysis:

The first parameter: the starting position of interception

The second parameter: the number of interceptions

After the second parameter: the inserted data, if there is no third parameter, it will not be inserted

2.6 slice method: Intercept the array, but do not operate on the array itself

var arr=[1,2,3,4,5];
var result =arr.slice(2,4);
console.log("arr:"+arr);
console.log("result:"+result);

Result:

arr:1,2,3,4,5
result:3,4

Analysis:

First one Parameter: The starting position of interception is a closed interval

The second parameter: The end position of interception is an open interval

Such as: [2,4)

2.7 concat method: Splice arrays, but do not operate on the array itself

var arr1 =[1,2,3];
var arr2=[3,4,5];
var result = arr1.concat(arr2);
console.log("arr1:"+arr1);
console.log("arr2:"+arr2);
console.log("result:"+result);

Result:

arr1:1,2,3
arr2:3,4,5
result:1,2,3,3,4,5

2.8 join method: For each element of the array Insert elements in between, but do not operate the array itself

var arr =[1,2,3];
var result =arr.join("-");
console.log("arr:"+arr);
console.log("result:"+result);

Result:

arr:1,2,3
result:1-2-3

2.9 reverse method: Reverse the position of the elements in the array

var arr =[1,2,3];
var result =arr.reverse();
console.log("arr:"+arr);

Result :

arr:3,2,1

2.10 sort method: Sort the elements in the array (defective)

var arr =[4,10,1,5];
var result =arr.sort();
console.log("arr:"+arr);

Result:

arr:1,10,4,5

Analysis:

In During the comparison process, this 10 is compared according to the first digit and then the second digit, so it is ranked behind 1 and in front of 4.

2.11 sort method expansion

var arr =[4,10,1,5];
        function  compare(value1,value2){//自定义排序规则
            if(value1>value2){
                return 1;
            }else if(value1<value2){
                return -1;
            }else{
                return 0;
            }
        }
        var result =arr.sort(compare);使用自定义的排序规则 实现从小到大排序 要想实现从大到小 修改排序规则
        console.log("arr:"+arr);

Result:

arr:1,4,5,10