js 的let 和const 的区别

1. const必须给变量赋值，否则会报错
2. let 可以不给变量赋值，结果为undefined

let a 
console.log(a) // undefined
const a
console.log(a) // 报错

1. const赋值不可变
2. let 赋值可变

let arr = [1,2,3];
    arr = [4,5,6]
    console.log(arr) //[ 4,5,6]
const arr = [1,2,3];
      arr = [4,5,6]
      console.log(arr) //报错，引用地址只能是一个