es6对es5有哪些方面的优化呢？

引入了let和const解决了var变量提升带来的问题，同时引入箭头函数解决this访问问题。

function Person(firstname, lastname) {    this.firstname = firstname;    this.lastname = lastname;}//输出undefinedPerson.prototype.getNameInCallback = function () {    setTimeout(functino(){        console.log(this.firstname, this.lastname);    }, 1000);}//输出heyanboPerson.prototype.getNameInCallback = function () {    setTimeout(functino(){        console.log(this.firstname, this.lastname);    }.bind(this), 1000);}//输出heyanboPerson.prototype.getNameInCallback = function () {let context = this;    setTimeout(functino(){        console.log(context.firstname, context.lastname);    }.bind(this), 1000);}//输出heyanboPerson.prototype.getNameInCallback = function () {    setTimeout(() => {      //箭头函数里面的this可以直接当成一个变量，直接从父级作用域链中等变量对象中获取        console.log(this.firstname, this.lastname);    }, 1000);}var p = new Person('he', 'yanbo');p.getNameInCallback();