Some methods of JS

Some methods of JS

indexOf

var str='abcdgdjfahgzk'
   console.log(str.indexOf('g'));//4
console.log(str.indexOf('l'));//-1

Whether the match has the same character, yes, return its position, no, return -1

join

join turns an array into a string

var str2=new Array();
str2=[5,4789,4,9,4,9,4,9,4,94]
console.log(str2.join(''));//54789494949494括号内为分隔条件，这里分隔为空

pop

pop() removes the last element from the array and returns it

var str2=new Array();
str2=[5,4789,4,9,4,9,4,9,4,94]
console.log(str2.pop());//94
console.log(str2);//[5, 4789, 4, 9, 4, 9, 4, 9, 4]

shift

shift() removes the first element from the array and returns that element

var str2=new Array();
str2=[5,4789,4,9,4,9,4,9,4,94]
console.log(str2.shift());//5
console.log(str2);//[4789, 4, 9, 4, 9, 4, 9, 4]

unshift

unshift() appends an element to the first index position in the array

str2.unshift(1);
   console.log(str2)//[1, 5, 4789, 4, 9, 4, 9, 4, 9, 4, 94]

for in

var ty={
	'name':'张三',
	'age':'20'
}
for(var items in ty){
 	console.log(items)//name,age
}

for Each

for Each traverses the array and returns two parameters, one content and one index

str2.forEach(function(items,index){
    
    
    console.log(items,index)
}

map

Creates a new array whose result is the result returned by calling a provided function on each element in the array, extremely fast,

The return result is true and false

var newarr=str2.map(function(item,index){
    
    
    return item<10;
})
console.log(newarr)
//10) [true, false, true, true, true, true, true, true, true, false]

delete

delete arr2[1]//不常用
//splice(index,deleteElementlenght,ele1,ele2,ele3);
var arr4=['I','LOVE','JAVAscript','caigui']
var arr5=arr4.splice(1,2,'get','change')//arr4中的1,2位置返回给arr5，用后面两个代替
//split()将字符串转换为数组
//slice()返回一个新的数组对象，左开右闭

sort

Sorting, if a is less than b, that is, a - b is less than zero, then return a value less than zero, and the array will be sorted in ascending order.

Returns 0 if a is equal to b.

If a is greater than b, that is, a - b is greater than zero, then return a value greater than zero, and the array will be sorted in descending order.

var arr = ['General','Tom','Bob','John','Army'];
var resArr = arr.sort();
console.log(resArr);//输出   ["Army", "Bob", "General", "John", "Tom"]

var arr2 = [30,10,111,35,1899,50,45];
var resArr2 = arr2.sort();
console.log(resArr2);//输出   [10, 111, 1899, 30, 35, 45, 50]
//不传参，按照字符编码的顺序排序

ar arr3 = [30,10,111,35,1899,50,45];
		arr3.sort(function(a,b){
    
    
			return a - b;//a小于b，升序
		})
		console.log(arr3);//输出  [10, 30, 35, 45, 50, 111, 1899]
		
		var arr4 = [30,10,111,35,1899,50,45];
		arr4.sort(function(a,b){
    
    
			return b - a;//a大于b，降序
		})
		console.log(arr4);//输出 [1899, 111, 50, 45, 35, 30, 10]