js笔记（if,switch,for,while,三元,func,obj,json,reg）

if

var a=10;
if (a>10){
    console.log('a>10')
}else if(a>5){
    console.log('5<a<=10')
}else {console.log('a<=5')};

switch

var num = 1 ;
switch (num){case 0 : console.log('case 0');break;
                      case 1 : console.log('case 1');break;
                      case 2 : console.log('case 2');break;
                      default: console.log('unmatched');}

for

for (let i=0;i<10;i++){console.log(i)}

l1=[111,222,333,444,555];
for (let i=0;i<l1.length;i++){console.log(l1[i])}

while

var i =0;
while(i<20){console.log(i); i++}

三元运算符

var aaa = 1<5 ?666:438
/*
判断条件：1<5
true返回？后面的值
false返回：后面的值
*/

function

function fun1(a,b){console.log(a,b)}
fun1('小马','老马','骏马','司马')
fun1('小马')
//参数数量不符不报错

function fun2(a,b){
if (arguments.length<2){console.log('错误：参数不足2个')}
else if (arguments.length>2){console.log('错误：参数超过2个')}
else {console.log(a,b)}
}

function fun3(){return 1,2,3}
//只返回一个值（只返回3）
function fun4(){return [1,2,3]}
//返回整个数组

箭头函数

var func1 = a => a;
//var function func1 (a){return a}
var func2 = (arg1,arg2) => arg1+arg2;

自定义对象（字典）

//第一种
var dic = {'name':'小马','age':73}

dic["name"]
dic.age
//第二种
var dic = new Object()
dic.name='老马'
dic.gender='male'

dic.gender

//for循环取值
for (let i in dic){console.log(i,dic[i])}

日期对象

var dd = new Date()

dd
dd.toLocaleString()
dd.toDateString()
dd.getDate()
dd.getDay()

json

	py	js
序列化	py ==> json dumps	js ==>json JSON.stringify()
反序列化	py <==json loads	js <==json JSON.parse()

 

 

 

 

 

 

 

var dic ={'name':'小马','age':84}

var dicS = JSON.stringify(dic)
dicS

JSON.parse(dic)

regexp

//第一种
let reg1 = new RegExp ('^[A-Z][a-z0-9]{3,6}')

//第二种
let reg2 = /^[A-Z][a-z0-9]{3,6}/

reg2.test('Azxc32')


let str = 'xiaoma laoma junma sima'
//只匹配1次
str.match(/ma/)
//匹配所有      
str.match(/ma/g)