ES6箭头函数与function有什么区别？

// function的写法

function fn(a, b){

    return a+b;

}

// 箭头函数的写法

let foo = (a, b) =>{ return a + b }

//使用function定义的函数

function foo(){

    console.log(this);

}

var obj = { aa: foo };

foo(); //Window

obj.aa() //obj { aa: foo }

//使用箭头函数定义函数

var foo = () => { console.log(this) };

var obj = { aa:foo };

foo(); //Window

obj.aa(); //Window

function Timer() {

  this.s1 = 0;

  this.s2 = 0;

  // 箭头函数

  setInterval(() => {

     this.s1++;

     console.log(this);

  }, 1000); // 这里的this指向timer

  // 普通函数

  setInterval(function () {

    console.log(this);

    this.s2++; // 这里的this指向window的this

  }, 1000);

}

var timer = new Timer();

setTimeout(() => console.log('s1: ', timer.s1), 3100);

setTimeout(() => console.log('s2: ', timer.s2), 3100);

// s1: 3

// s2: 0

//使用function方法定义构造函数

function Person(name, age){

    this.name = name;

    this.age = age;

}

var lenhart =  new Person(lenhart, 25);

console.log(lenhart); //{name: 'lenhart', age: 25}

//尝试使用箭头函数

var Person = (name, age) =>{

    this.name = name;

    this.age = age;

};

var lenhart = new Person('lenhart', 25); //Uncaught TypeError: Person is not a constructor

foo(); //123

function foo(){

    console.log('123');

}

arrowFn(); //Uncaught TypeError: arrowFn is not a function

var arrowFn = () => {

    console.log('456');

};

console.log(f1); //function f1() {}  

console.log(f2); //undefined 

function f1() {}

var f2 = function() {}