为什么var不好

1 有预解析

2 没有块级结构

解构

对象解构

//对象到变量
//变量到对象

        let obj = {
            name: 'lhy',
            age: 21,
            sex: 'F'
        }

        let { name, age, sex } = obj
        console.log({ name, age, sex })

        let name1 = 'lhy'
        let age1 = 21
        let sex1 = 'F'

        let obj1 = { name1, age1, sex1 }
        console.log(obj1)

数组解构

//数组到变量
//变量到数组
        let arr = [10, 20, 30]

        let [n1, n2, n3] = arr
        console.log([n1, n2, n3])

        let k1 = 10
        let k2 = 20
        let k3 = 30
        let arr1 = [k1, k2, k3]
        console.log(arr1)

函数解构

function fn({ name, age, sex }) {
            console.log({ name, age, sex })
        }

        fn({ name: 'lhy', age: 21, sex: 'F' })