ES6中的let与var的区别

if (true) {
    var a = 1;
    let b = 2;
}
console.log(a);  //输出1
console.log(b);  //b is not defined

if (true) {
   var a = 1;
   let b = 2;
   console.log(a); //输出1
   console.log(b); //输出2  let只能在特定的区域中使用
}