Explain the JavaScript built-in object Array (array)

Explain the JavaScript built-in object Array (array)

1. Two ways to create an array

Method one: array literal

var arr=[1,2,3,4,5,6];

Method 2: new Array()

var arr1=new Array();   //创建一个空数组
var arr2=new Array(2);  //创建一个长度为2的数组
var arr3=new Array(2,3,4);   //创建一个[2,3,4]的数组

Two. Two methods to detect whether it is an array

Method one: instanceof operator

var arr4=[1,2,3,4,5];
console.log(arr4 instanceof Array);    //true
var arr5={};
console.log(arr5 instanceof Array);    //false

Method 2: Array.isArray (parameter)

console.log(Array.isArray(arr4));      //true
console.log(Array.isArray(arr5));      //false 

Three. Add and delete the method of array elements

1. push() (add one or more elements to the end of the original array, the return value is the length of the new array)
2. unshift() (add one or more elements at the beginning of the original array, the return value is the length of the new array)
3. pop() (delete the last element of the original array, the return value is the deleted element)
4. shift() (delete the first element of the original array, the return value is the deleted element)

var arr6=[1,2,3,4,5];
console.log(arr6.push(6,7)); //7
console.log(arr6.unshift(-1,0)); //9
var arr7=[1,2,3,4,5,6,7];
console.log(arr7.pop()); //7
var arr8=[3,4,5,6,7,8,9];
console.log(arr8.shift());  //3

Four. Array index method

1. indexOf() (only the index of the first element is satisfied, if no element is found, -1 is returned)
2. lastIndexOf() (search from back to front, return -1 if not found)

var arr12=['red','blue','yellow','green','pink','yellow'];
console.log(arr12.indexOf('pink')); //4
console.log(arr12.lastIndexOf('yellow')); //5