//Number 数值 整数和小数
//string 字符串 (字符) "" ''
//Bool   true/false
//null   没有
//undefined  

var a=null;
console.log(typeof a);

// object: 正则、数组 字面量(json对象)
// function  

// json xml
//序列化 反序列化
//JSON.stringify()
//JSON.parse()
var stu = JSON.parse('{ "id":10001,"name":"张三"}')
console.log(stu.id)

var a=10;
{
    console.log(a);
    a=20;
}

// + - * /
var a = 3-"1";
console.log(a)

var a=(0.1*10+0.2*10)/10
console.log(a==0.3)

// = == ===
console.log(a=2);
console.log(a=="2");
console.log(a==="2");
console.log(a===3);
console.log(a===2);
 
 
// parseInt 取整 81.5 81
// parseFloat
// isNaN Not a number

var a = parseInt("8a6.99");
console.log(a);

var a = parseInt(85.5+0.5);
console.log(a);

function sum(a,b){
    return a+b;
}
var a = sum(3,4);
console.log(a);

function sum(a){
    console.log(arguments)
    console.log(a)
    // ...
    return 1;
}

var a = sum(3,4,5,6,7)
console.log(a);

var arr=new Array(2);
arr[0]=0;
arr[1]=1;
arr[1]=1;
console.log(arr)

var arr=[1,"2",3,function(){}]
console.log(arr)

//arr.shift()
//arr.unshift()
//arr.push()
//arr.pop()

var arr=[1,2,3,4,5]
//arr.unshift(2)
//console.log(arr,res)
//开始位置  删除个数  ...添加数据
arr.splice(2,1,8)
console.log(arr)