es6对es5有哪些方面的优化呢？

Answer 1

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undefined
Person.prototype.getNameInCallback = function () {
    setTimeout(functino(){
        console.log(this.firstname, this.lastname);
    }, 1000);
}
//输出heyanbo
Person.prototype.getNameInCallback = function () {
    setTimeout(functino(){
        console.log(this.firstname, this.lastname);
    }.bind(this), 1000);
}
//输出heyanbo
Person.prototype.getNameInCallback = function () {
let context = this;
    setTimeout(functino(){
        console.log(context.firstname, context.lastname);
    }.bind(this), 1000);
}
//输出heyanbo
Person.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();