1、let的用法
1、
//查看js的引入路径是否正确
console.log("1:",1)
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422211132259-1981581031.png)
2、
var a=1;
let b=2;
console.log("a:",a)
console.log("b:",b)
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422211236024-1500681165.png)
3、
if(true)
{
var a=1;
let b=2;
}
console.log("a:",a)
console.log("b:",b)
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422211538618-197310454.png)
4、
if(1)
{
let b=2;
console.log("b:",b)
}
console.log("b:",b)
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422211920227-861259024.png)
5、
for(let i=0;i<3;i++)
{
console.log("i:",i)
}
console.log("i:",i)
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422212155290-950894147.png)
6、ES5变量提升问题
var a=1;
function foo() {
if(false)
{
var a=1;
}
console.log("a:",a)
}
foo();
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422212447977-231128033.png)
7、
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422212750024-1284212883.png)
console.log("a:",a)
var a;
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422212839556-2047990633.png)
console.log("a:",a)
let a;
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422212941165-1504035645.png)
2、const的用法
1、
const love_you=true;
love_you=false;
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422213431899-1561285536.png)
2、常量需要声明时赋值
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422213621493-1721539453.png)
3、
let user={name:'王花花',age:10}
const Love_you=user;
console.log(Love_you)
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422213955071-1431556161.png)
let user={name:'王花花',age:10}
const Love_you=user;
console.log(Love_you)
love_you=1;
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422214207899-736392553.png)
4、
let user={name:'王花花',age:10}
const Love_you=user;
console.log(Love_you)
user.age=12;
console.log(Love_you)
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422214332337-354052120.png)
let user={name:'王花花',age:10}
const Love_you=user;
console.log(Love_you)
Love_you={};
console.log(Love_you)
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422214529556-2011805331.png)
var user={name:'王花花',age:10}
const Love_you=user;
console.log(Love_you)
![](https://images2015.cnblogs.com/blog/612158/201704/612158-20170422214701696-1532990413.png)