//声明变量 let a; let b,c,d; let e = 100; let f = 521, g = 'iloveyou', h = []; //1. 变量不能重复声明 let star = '罗志祥'; let star = '小猪'; //2. 块儿级作用域 全局, 函数, eval 读取不到girl变量,因为超出作用域了 // if else while for { let girl = '周扬青'; } console.log(girl); //3. 不存在变量提升 会报错 console.log(song); let song = '恋爱达人'; //4. 不影响作用域链 { let school = '尚硅谷'; function fn(){ console.log(school); } fn(); }