JS array operations (pop, push, unshift, splice, shift methods)

What they change is the length and content of the original array , If you set a new element outside to receive his changes , Then this element can only get the length after it is processed .

pop Finally delete

var a = [1,2,3,4,5];

var b = a.pop();    //a：[1,2,3,4] b：5

pop Final addition

var a = [1,2,3,4,5];

var b = a.push(6,7); //a：[1,2,3,4,5,6,7] b：7

shift Delete at the beginning

var a = [1,2,3,4,5];

 var b=a.shift();   //a :[2,3,4,5] b:1

unshift Add... At the beginning

var a = [1,2,3,4,5];

 var b=a.unshift(-2,-1);  //a: [-2,-1,1,2,3,4,5] b：7  This 7 yes a The length of 

concat Concatenate two arrays

var a = [1,2,3,4,5];

var b = a.concat(6,7);  //a：[1,2,3,4,5,6,7] b：7

splice(start,deleteCount,val1,val2,…) From the subscript for start To delete deleteCount Elements , And add val,val2 ...

var a = [1,2,3,4,5];

var b = a.splice(2,2,7,8,9); 
console.log(b);
console.log(a);


VM618:4 (2) [3, 4]
VM618:5 (6) [1, 2, 7, 8, 9, 5]

reverse： Reverse the array

var a = [1,2,3,4,5];

a.reverse()  //5,4,3,2,1

sort(orderfunction)： Sort the array by the specified parameters

var a = [1,2,3,4,5];

a.sort()  //1,2,3,4,5 positive sequence 

slice(start,end)： Returns a new array of items from the specified start subscript to the end subscript in the original array

   var a = [1,2,3,4,5];

   a.slice(1,4)//2,3,4,5