1. Use strict added in ES 5 use this for Vanila Javascript. 'use strict'; 2. Variable, rw(read/write) let (added in ES6) let globalName = 'global name'; { let name = 'ellie'; console.log(name); name = 'hello'; console.log(name); console.log(globalName); } console.log(name); //->{ } 내부에서 정의된 변수는 외부에서 찾을 수 없음 console.log(globalName); //어디서든 가능 var (don't ever use this!) - var hoisting: (move decla..