Reference: https://stackoverflow.com/questions/1684917/what-questions-should-a-javascript-programmer-be-able-to-answer
class User { constructor(name) { this.name = name; } }
http://jsrun.net/QpbKp/edit
The difference is scoping. var is scoped to the nearest function block and let is scoped to the nearest enclosing block.
http://jsfiddle.net/questwork/nfb7B/
https://jsfiddle.net/questwork/10497gs8/
假设你要做一个图书管理系统。你会怎样设计 MongoDB document 以达到以下需求?