Detailed introduction to arrays in javaScript

Create array

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

var arr=new Array()

##　var arr=new Array(10);//Create an array with a length of 10

　

var arr =new Array(1,2,3,4,5,6);//Create an array

arr.length==6;

Delete array delete var a=[1,2,3];

delete a[0];

　1 in a //false,

##　a.length //3, delete operation will not affect the length of the array

Array traversal

##　

for/in forEach　　var a=[1,2,3];

　　var b=0;

　　a. forEach(function(x){

##　　b+=x;//Add

　　})

Array methods

Array.jion();//Convert all elements to strings and concatenate them together, default comma Connection, there is a parameter, you can modify the connection style

Array.reverse();//Reverse sort the array

Array.sort(); // Sort the array and return the sorted array. If there are no parameters, the default alphabetical order will be used. If there are parameters, the order will be confirmed based on the return value of the callback function.

　

　var a=[33,4,1111,222];　　a.sort();//1111,222,33,4;

　　a.sort(function(a,b){

　　　return a-b;//4,33,222,1111

　　});

　　a.sort(function(){

　　　　return b-a;//1111,222,33,4

　　　})

Array.concat();//Concatenate arrays

var a=[1,2,3];

　a.concat(4,5);//[1,2,3,4,5]　a.concat([ 4,5]);//[1,2,3,4,5]

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

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

Array.slice(); returns a fragment of the specified array

　　

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

##　　a .slice(0,3);//[1,2,3,4];

## a.slice(3);//[4,5];

##　a.slice(1,-1);//[2,3,4];

#　a.slice(-3,-2);//[3]

# Array.splice() ;splice() will modify the array. The first parameter is the starting point, the second parameter is the number of deleted items, and the subsequent parameters are the inserted elements. The starting point of the inserted elements is the first parameter. Note that the inserted array is an array. Itself, not the elements inside

Array.push( ) and Array.pop(); push adds elements at the end, pop deletes elements at the end, and modifies the original array

##　##Array.unshift() and Array.shift(); unshift adds elements to the head, shift deletes elements to the head, and modifies the original array

Array.toString() and Array.toLocalString(); convert to string

#Array methods in ES5

forEach() method

Map() method

　##var a=[1,2,3]; b=a.map(function(x){ return x*x;//b is [1,4,9]　　})

## Filter()

　## var a=[5,4,3,2,1];　b=a.filter(function(x){

Return x<3;//[2,1]

##　　})

## var a=[5,4,3,2,1];##　b=a.filter(function(x,i){

Return i%2==0;//[5,3,1], i is the second parameter of filter, it represents the subscript of the array, and there is a third parameter The current element belongs to the object of the array

##　　})

##　every() and some(); are logical judgments of the array

##　　

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

## b=a.every(function(x){

return x<10;// true;

　　})

　　　

var a=[5,4,3,2,1];## b=a .some(function(x){

Return x%2===0;//false;

　　})

　

reduce() and reduceRight()

　　

var a=[5,4,3,2,1];# b=a.reduce(function(x,y){ 　　　return x+y;//Array summation

　　},0)

b=a.reduce(function(x,y){

## return x*y;//Array multiplication

　　},1)

##　　b=a.reduce(function(x,y){

Return x>y?x:y;//Find the minimum value 　　},1)

　　reduce()//Two parameters, the first parameter executes the function, the second parameter Optional initial value. When the function is executed for the first time, the initial value is used as the first parameter of the function. The value returned by subsequent executions of the function is used as the first parameter of the function.

　　reduceRight() and Like reduce(), execution starts from the last element

indexOf() and lastindexOf; search for the specified element of the array, if found return the subscript, if not found return -1

Type of array

##　Array.isArray([]);/ /true

　Array.isArray([]);//false

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