Methods in arrays

Today we will talk about several methods of operating on arrays:

//Add

a =[];//Empty array
a[0]="I am the first";
a[2]="I am the third";
a[10]="I It is the eleventh one";
alert(a.length);//11

//Delete
var a=[1,2,3,4,5];
delete a[4]//Delete the fifth element, but do not delete the position
alert(a.length);

//Add one at the end of push() or more, and return the new length
a=[1,2,3];
alert(a..push("二狗","男",20));//Add to the end of the array One or more
alert(a.length);
alert(a[0]);

//pop() removes and returns the last element of the array.
//Syntax arr.pop();
//Return value The last element of arr.
var arr=new Array(3);//The length is 3
arr[0]="George";
arr[1]="John";
arr[2]=" Thomas";
document.write(arr)
document.write("
")
document.write(arr.pop())//Delete and return the last item in the array element.
document.write("
")
document.write(arr)

//unshift() Add one or more elements to the beginning of the array, and Return the new length
a=[1,2,3];
a.unshift("二狗","男",20);//Add one or more to the end of the array
alert (a.length);
alert(a[0]);

//shift() delete and return the first element
var arr=new Array(3);
arr[0]="George";
arr[1]="John";
arr[2]="Thomas";
document. write(arr)
document.write("
")
document.write(arr.shift())//Delete and return the first element
document.write("
")
document.write(arr)

//concat() method merges two or more arrays

var a=[1,2,3,4,5];
var b=[6,7,8,9,10];
var c=[11,12,13,14,15 ]
alert(b.concat(a,c));

//join() converts all elements in the array into strings And connected together

var arr=["Today is Friday", "Tomorrow is a holiday", "The day after tomorrow is also a holiday"]
alert(arr.join(","));
alert (typeof arr.join(""))

//revese()The elements are reversed in order

var arr=["Today is Friday", "Tomorrow is a holiday", "The day after tomorrow is also a holiday"];
alert(arr.reverse())

//The slice method intercepts a part of the array,
//The first parameter is the subscript at the beginning of the array, and the corresponding element must be subscripted
//The second parameter is the subscript at the end of the array, but not Corresponding element

a=[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
alert(a.slice (0,10))
alert(a.slice(-15,-5))
alert(a)//Still the original array has not changed

//sort() sorts the array elements

var a=[1,9,5,12,24,16]
function hanshu(x,y){
return x-y;
}

alert(a.sort(hanshu))

//splice( ) is used to insert, delete or replace elements of the original array

a=[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15] ;
a.splice(4,6)//Delete 6 starting from the fifth one
alert(a)
a.splice(4,6,50,60,70,80,90,100,110,120,130,140) //Delete 6 numbers starting from the fifth one and add the following numbers
alert(a)

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