js中let和var的区别

if (true) {

  var name = 'Stan'

  console.log(name) // Stan

}

console.log(name) // Stan

if (true) {

  let age = 20 // 作用域仅限于当前块

  console.log(age) // 20

}

console.log(age) // ReferenceError

console.log(name) // undefined

console.log(age) // ReferenceError

var name = 'xiaoming'

let age = 20