es5 function函数转换es6箭头函数

例如：

var users = [
  {name: "路飞", "email": "lufei@email.com"},
  {name: "索隆",   "email": "suolong@email.com"},
  {name: "娜美",  "email": "namei@email.com"}
];
var emails = users.map( function(user) { return user.email; });
console.log(emails.join(", "));

console.log

lufei@email.com, suolong@email.com, namei@email.com

修改后:

var users = [
  {name: "路飞", "email": "lufei@email.com"},
  {name: "索隆",   "email": "suolong@email.com"},
  {name: "娜美",  "email": "namei@email.com"}
];
var emails = users.map( (user)=> { return user.email; });
console.log(emails.join(", "));

输出

 lufei@email.com, suolong@email.com, namei@email.com