var f = () => 5;
// 等同于
var f = function () { return 5 };
var sum = (num1, num2) => num1 + num2;
var sum = (num1, num2) => { return num1 + num2};
// 等同于
var sum = function(num1, num2) {
return num1 + num2;
};
原文：https://www.cnblogs.com/geekjsp/p/9868079.html