[转] Node.js 框架比较: Express vs. Koa vs. Hapi

英文原文：Node.js Framework Comparison: Express vs. Koa vs. Hapi
作者：Jonathan
译者：戴嘉华
原文地址：Node.js 框架比较: Express vs. Koa vs. Hapi

1 Introduction

Express.js is the most popular Node.js web application framework used today. It seems to be the base dependency in most Node.js web applications, even some popular frameworks like Sails.js are built off of Express. However there are more options available that have the same “sinatra-like” feel to them. The next two most popular frameworks are Koa and Hapi respectively.
This is not going to persuade you to use one framework over the other, it’s merely going to help you get a better understanding of what each framework can do and where one might trump the other.

Express.js无疑是当前Node.js中最流行的Web应用程序框架。它几乎成为了大多数Node.js web应用程序的基本的依赖，甚至一些例如Sails.js这样的流行的框架也是基于Express.js。然而你还有一些其他框架的选择，可以给你带来“sinatra”一样的感觉（译注：sinatra是一个简单的Ruby的Web框架，可以参考这篇博文）。另外两个最流行的框架分别是Koa和Hapi。

这篇文章不是打算说服你哪个框架比另外一个更好，而是只是打算让你更好地理解每个框架能做什么，什么情况下一个框架可以秒杀另外一个。

2 Framework backgrounds

All three of the frameworks we will be looking at have a lot in common. All can create a server with just a few lines of code and all make creating a REST API very simple. Lets look at how these frameworks began.

框架的背景。我们将要探讨的两个框架看起来都非常相似。每一个都能够用几行代码来构建一个服务器，并都可以非常轻易地构建REST API。我们先瞧瞧这几个框架是怎么诞生的。

2.1 Express

The initial commit for Express was made on June 26, 2009 by TJ Holowaychuk and 660 commits later version 0.0.1 was released on January 2, 2010. The two main contributors at that time were TJ and Ciaron Jessup. At the time of the first release the framework was described as per the readme.md on github
Insanely fast (and small) server-side JavaScript web development framework built on node.js and V8 JavaScript engine.
Fast forward almost 5 years and 4,925 commits, now 4.10.1 is the latest version maintained by StrongLoop as TJ is now concentrating in the Go-Lang community.

2009年6月26日，TJ Holowaychuk提交了Express的第一次commit，接下来在2010年1月2日，有660次commits的Express 0.0.1版本正式发布。TJ和Ciaron Jessup是当时最主要的两个代码贡献者。在第一个版本发布的时候，根据github上的readme.md，这个框架被描述成：

疯一般快速（而简洁）的服务端JavaScript Web开发框架，基于Node.js和V8 JavaScript引擎。
差不多5年的时间过去了，Express拥有了4,925次commit，现在Express的最新版本是4.10.1，由StrongLoop维护，因为TJ现在已经跑去玩Go了。

2.2 Koa

The initial commit for Koa was just over a year ago on August 17, 2013 by none other than TJ Holowaychuk. He describes it as “Expressive middleware for node.js using generators via co to make writing web applications and REST APIs more enjoyable to write”. Koa is advertised as having a small footprint of ~400 SLOC. It is now on version 0.13.0 with 585 commits.

大概在差不多一年前的2013年8月17日，TJ Holowaychuk（又是他！）只身一人提交了Koa的第一次commit。他描述Koa为“表现力强劲的Node.js中间件，通过co使用generators使得编写web应用程序和REST API更加丝般顺滑”。Koa被标榜为只占用约400行源码空间的框架。Koa的目前最新版本为0.13.0，拥有583次commits。

2.3 Hapi

The initial commit for Hapi was on August 5, 2011 by Eran Hammer a member of WalmartLabs. Hapi was created by parts of Postmile and was originally built on top of Express. Later it was developed into its own framework because of what Erin state’s in his blog:
hapi was created around the idea that configuration is better than code, that business logic must be isolated from the transport layer…
3,816 commits later Hapi is is on version 7.2.0 and is still maintained by Eran Hammer.

2011年8月5日，WalmartLabs的一位成员Eran Hammer提交了Hapi的第一次commit。Hapi原本是Postmile的一部分，并且最开始是基于Express构建的。后来它发展成自己自己的框架，正如Eran在他的博客里面所说的：

Hapi基于这么一个想法：配置优于编码，业务逻辑必须和传输层进行分离..
Hapi最新版本为7.2.0，拥有3,816次commits，并且仍然由Eran Hammer维护。
最后我们一起来看看关于这几个流行的框架的社区数据：

Metric	Express.js	Koa.js	Hapi.js
Github Stars	16,158	4,846	3,283
Contributors	163	49	95
Packages that depend on	3,828	99	102
StackOverflow Questions	11,419	72	82

3 Creating a server

The first step for any developer when working on a Node.js web application is to create a basic server. So lets create a server using each framework to see their similarities and differences.

所有开发者要开发Node.js web应用程序的第一步就是构建一个基本的服务器。所以我们来看看用这几个框架构建一个服务器的时候有什么异同。

3.1 Express

This is probably pretty natural to all node developers. We require express and then instantiate it by assigning it to the variable app. Then instantiate a server to listen to a port, port 3000. The app.listen() is actually just a wrapper around node’s http.createServer().

var express = require('express');
var app = express(); 
var server = app.listen(3000, function() { 
    console.log('Express is listening to http://localhost:3000'); 
});

对于所有的node开发者来说，这看起来相当的自然。我们把express require进来，然后初始化一个实例并且赋值给一个为app的变量。接下来这个实例初始化一个server监听特定的端口，3000端口。app.listen()函数实际上包装了node原生的http.createServer()函数。

3.2 Koa

Right away you can see that Koa is similar to Express. Essentally you just required koa instead of express. Also app.listen() is the exact same wrapper function as used in Express.

var koa = require('koa');
var app = koa();

var server = app.listen(3000, function() {
    console.log('Koa is listening to http://localhost:3000');
});

你马上发现Koa和Express是很相似的。其实差别只是你把require那部分换成koa而不是express而已。app.listen()也是和Express一模一样的对原生代码的封装函数。

3.3 Hapi

Hapi is the unique one of the group. First like always, hapi is required but instead of instantiating a hapi app, you create a new Server and specify the port. In Express and Koa we get a callback function but in Hapi we get a new server object. Then once we call server.start() we start the server on port 3000 which then returns a callback. However this is not like Koa and Express, it is not a wrapper around http.CreateServer(), it is using it’s own logic.

var Hapi = require('hapi');
var server = new Hapi.Server(3000);

server.start(function() {
    console.log('Hapi is listening to http://localhost:3000');
});

Hapi是三者中最独特的一个。和其他两者一样，hapi被require进来了但是没有初始化一个hapi app而是构建了一个server并且指定了端口。在Express和Koa中我们得到的是一个回调函数而在hapi中我们得到的是一个新的server对象。一旦我们调用了server.start()我们就开启了端口为3000的服务器，并且返回一个回调函数。这个server.start()函数和Koa、Express不一样，它并不是一个http.CreateServer()的包装函数，它的逻辑是由自己构建的。

4 Routes

Now lets dig into one of the most important features of a server, routing. First lets create the cliche “Hello world” application for each framework and then move on to something a little more useful, REST API.

现在一起来搞搞一下服务器最重要的特定之一，路由控制。我们先用每个框架分别构建一个老掉渣的“Hello world”应用程序，然后我们再探索一下一些更有用的东东，REST API。

4.1 Hello world

4.1.1 Express

We are using the get() method to catch the incoming request of “GET /” and then invoke a callback function that handles two parameters req and res. For this example we are only utilizing res to return back to the page a string using res.send(). Express has a variety of built in methods that are used to handle the routing functionality. The following are some of the more commonly used methods that are supported by Express (but not all of the methods): get, post, put, head, delete…

var express = require('express');
var app = express();

app.get('/', function(req, res) {
    res.send('Hello world');
});

var server = app.listen(3000, function() {
    console.log('Express is listening to http://localhost:3000');
});

我们用get()函数来捕获“GET /”请求然后调用一个回调函数，这个回调函数会被传入req和res两个对象。这个例子当中我们只利用了res的res.send()来返回整个页面的字符串。Express有很多内置的方法可以用来进行路由控制。get, post, put, head, delete等等这些方法都是Express支持的最常用的方法（这只是一部分而已，并不是全部）。

4.1.2 Koa

Koa is slightly different than Express, it is using ES6 generators. Any function preceded by a * means the function will return a generator object. Basically these generators yield values synchronously but that is beyond the scope of this post. Within the app.use() the generator function sets the response body. In Koa the Context which is equivalent to the this identifier is an encapsulation of node’s request and response objects. this.body is a method in the Koa Response object. this.body can be set to a string, buffer, stream, object, or null. This example we used one of the few middlewares provided in the Koa core. This middleware we used catches all routes and responds with the string provided.

var koa = require('koa');
var app = koa();

app.use(function *() {
    this.body = 'Hello world';
});

var server = app.listen(3000, function() {
    console.log('Koa is listening to http://localhost:3000');
});

Koa和Express稍微有点儿不同，它用了ES6的generators。所有带有*前缀的函数都表示这个函数会返回一个generator对象。根本上来说，generator会同步地yield出数据（译注：如果对Python比较熟悉的话，应该对ES6的generator不陌生，这里的yield其实和Python的yield语句差不多一个意思），这个超出本文所探索的内容，不详述。在app.use()函数中，generator函数设置响应体。在Koa中，this这个上下文其实就是对node的request和response对象的封装。this.body是KoaResponse对象的一个属性。this.body可以设置为字符串, buffer, stream, 对象, 或者null也行。上面的例子中我们使用了Koa为数不多的中间件的其中一个。这个中间件捕获了所有的路由并且响应同一个字符串。

4.1.3 Hapi

Here we are using the built in method that the server object provides us server.route() which has the following options: path(required), method(required), vhost, and handler(required). The HTTP method can handle the typical requests GET, PUT, POST, DELETE, and * which catches any route. The handler is passed a reference to the request object and must call reply with the containing payload. The payload can be a string, a buffer, a serializable object, or a stream.

var Hapi = require('hapi');
var server = new Hapi.Server(3000);

server.route({
    method: 'GET',
    path: '/',
    handler: function(request, reply) {
        reply('Hello world');
    }
});

server.start(function() {
    console.log('Hapi is listening to http://localhost:3000');
});

这里使用了server对象给我们提供的server.route内置的方法，这个方法接受配置参数：path（必须），method（必须），vhost，和handler（必须）。HTTP方法可以处理典型的例如GET、PUT、POST、DELETE的请求，*通配符可以匹配所有的路由。handler函数被传入一个request对象的引用，它必须调用reply函数包含需要返回的数据。数据可以是字符串、buffer、可序列化对象、或者stream。

4.2 REST API

The Hello world never really does much except show the most basic/simplest way to get an application up and running. REST APIs are almost a must in all data heavy applications and will help better understand how these frameworks can be used. So let’s take a look at how each handles REST APIs.

Hello world除了给我们展示了如何让一个应用程序运行起来以外几乎啥都没干。在所有的重数据的应用程序当中，REST API几乎是一个必须的设计，并且能让我们更好地理解这些框架是可以如何使用的。现在让我们看看这些框架是怎么处理REST API的。

4.2.1 Express

So we added our REST API to our existing Hello World application. Express offers a little shorthand for handling routes. This is Express 4.x syntax but it is essentially the same in Express 3.x except you don’t need the express.Router() and you will not be able to use the line app.use(‘/api’, router). Instead you will replace the router.route()’s with app.route() while prepending the existing verb with /api. This is a nice approach because it reduces the chance of developer errors and minimizes the places to change the HTTP method verbs.

var express = require('express');
var app = express();
var router = express.Router();    

// REST API
router.route('/items')
.get(function(req, res, next) {
  res.send('Get');
})
.post(function(req, res, next) {
  res.send('Post');
});

router.route('/items/:id')
.get(function(req, res, next) {
  res.send('Get id: ' + req.params.id);
})
.put(function(req, res, next) {
  res.send('Put id: ' + req.params.id);
})
.delete(function(req, res, next) {
  res.send('Delete id: ' + req.params.id);
});

app.use('/api', router);

// index
app.get('/', function(req, res) {
  res.send('Hello world');
});

var server = app.listen(3000, function() {
  console.log('Express is listening to http://localhost:3000');
});

我们为已有的Hello World应用程序添加REST API。Express提供一些处理路由的便捷的方式。这是Express 4.x的语法，除了你不需要express.Router()和不能用app.user(‘/api’, router)以外，其实上是和Express 3.x本质上是一样的。在Express 3.x中，你需要用app.route()替换router.route()并且需要加上/api前缀。Express 4.x的这种语法可以减少开发者编码错误并且你只需要修改少量代码就可以修改HTTP方法规则。

4.2.2 Koa

It’s pretty obvious that Koa doesn’t have the ability to reduce the repetitive route verbs like Express. It also requires a separate middleware to handle routes. I chose to use koa-route because it is maintained by the Koa team but there are a lot of routes available to use by other maintainers. The routes are very similar to Express with using the same keywords for their method calls like .get(), .put(), .post(), and .delete(). One advantage Koa has with handling its routes, is that it is using the ES6 generator functions which helps reduce the handling of callbacks.

var koa = require('koa');
var route = require('koa-route');
var app = koa();

// REST API
app.use(route.get('/api/items', function*() {
    this.body = 'Get';
}));
app.use(route.get('/api/items/:id', function*(id) {
    this.body = 'Get id: ' + id;
}));
app.use(route.post('/api/items', function*() {
    this.body = 'Post';
}));
app.use(route.put('/api/items/:id', function*(id) {
    this.body = 'Put id: ' + id;
}));
app.use(route.delete('/api/items/:id', function*(id) {
    this.body = 'Delete id: ' + id;
}));

// all other routes
app.use(function *() {
    this.body = 'Hello world';
});

var server = app.listen(3000, function() {
  console.log('Koa is listening to http://localhost:3000');
});

很明显，Koa并没有类似Express这样的可以减少编码重复路由规则的能力。它需要额外的中间件来处理路由控制。我选择使用koa-route因为它是由Koa团队维护的，但是还有很多由其他开发者维护的可用的中间件。Koa的路由和Express一样使用类似的关键词来定义它们的方法，.get(), .put(), .post(), 和 .delete()。Koa在处理路由的时候有一个好处就是，它使用ES6的generators函数来减少对回调函数的处理。

4.2.3 Hapi

First impressions of the routes in Hapi are how clean and readable they are compaired to the other frameworks. Even the required options method, path, handler, and replay for the routes are easy to the eye. Like Koa, there is a lot of reuse of code making the room for error larger. However this is intention, Hapi is more concerned about configuration and wants the code to be cleaner for easier use in a team. Hapi also wanted to improve error handling which it does without any code being written on the developers end. If you try to hit a route not described in the REST API it will return a JSON object with a status code and error description.

var Hapi = require('hapi');
var server = new Hapi.Server(3000);

server.route([
  {
    method: 'GET',
    path: '/api/items',
    handler: function(request, reply) {
      reply('Get item id');
    }
  },
  {
    method: 'GET',
    path: '/api/items/{id}',
    handler: function(request, reply) {
      reply('Get item id: ' + request.params.id);
    }
  },
  {
    method: 'POST',
    path: '/api/items',
    handler: function(request, reply) {
      reply('Post item');
    }
  },
  {
    method: 'PUT',
    path: '/api/items/{id}',
    handler: function(request, reply) {
      reply('Put item id: ' + request.params.id);
    }
  },
  {
    method: 'DELETE',
    path: '/api/items/{id}',
    handler: function(request, reply) {
      reply('Delete item id: ' + request.params.id);
    }
  },
  {
    method: 'GET',
    path: '/',
    handler: function(request, reply) {
      reply('Hello world');
    }
  }
]);

server.start(function() {
  console.log('Hapi is listening to http://localhost:3000');
});

对于Hapi路由处理的第一印象就是，相对于其它两个框架，这货是多么的清爽，可读性是多么的棒！即使是那些必须的method，path，handler和reply配置参数都是那么的赏心悦目（译注：作者高潮了）。类似于Koa，Hapi很多重复的代码会导致更大的出错多可能性。然而这是Hapi的有意之为，Hapi更关注配置并且希望使得代码更加清晰和让团队开发使用起来更加简便。Hapi希望可以不需要开发者进行编码的情况下对错误处理进行优化。如果你尝试去访问一个没有被定义的REST API，它会返回一个包含状态码和错误的描述的JSON对象。

5 The Good and The Bad

5.1 Express

5.1.1 The Good

Express has the biggest community not only out of the three frameworks compared here but out of all the web application frameworks for Node.js. It is the most matured framework out of the three, with almost 5 years of development behind it and now has StrongLoop taking control of the repository. It offers a simple way to get a server up and running and promotes code reuse with it’s built in router.

Express拥有的社区不仅仅是上面三者当中最大的，并且是所有Node.js web应用程序框架当中最大的。在经过其背后差不多5年的发展和在StrongLoop的掌管下，它是三者当中最成熟的框架。它为服务器启动和运行提供了简单的方式，并且通过内置的路由提高了代码的复用性。

5.1.2 The Bad

There is a lot of manual tedious tasks involved in Express. There is no built in error handling, it is easy to get lost in all of the middleware that could be added to solve a solution, and there are many ways to do one thing. Express describes itself as being opinionated, this could be good or bad but for beginning developers who must likely chose Express, this is a bad thing. Express also has a larger foot print compared to the other frameworks.

使用Express需要手动处理很多单调乏味的任务。它没有内置的错误处理。当你需要解决某个特定的问题的时候，你会容易迷失在众多可以添加的中间件中，在Express中，你有太多方式去解决同一个问题。Express自诩为高度可配置，这有好处也有坏处，对于准备使用Express的刚入门的开发者来说，这不是一件好的事情。并且对比起其他框架来说，Express体积更大。

5.2 Koa

5.2.1 The Good

Koa has a small footprint, it is more expressive and it makes writing middleware a lot easier than the other frameworks. Koa is basically a barebone framework where the developer can pick (or write) the middleware they want to use rather than compromising to the middleware that comes with Express or Hapi. It’s the only framework embracing ES6, for instance its using ES6 generators.

Koa有着傲人的身材（体积小），它表现力更强；对比起其他框架，它使得中间件的编写变的更加容易。Koa基本上就是一个只有骨架的框架，你可以选择（或者自己写一个）中间件，而不用妥协于Express或者Hapi它们自带的中间件。它也是唯一一个采用ES6的框架，例如它使用了ES6的generators。

5.2.2 The Bad

Koa is still unstable and heavily in development. Using ES6 is still ahead of the game for example version 0.11.9+ of Node.js needs to be used to run Koa and right now the latest stable version on Node.js is version 0.10.33. One thing that is in the good but could also be in the bad much like Express is the option of selecting multiple middlewares or writing your own middleware. Such as the router we looked at earlier, there are a lot of middleware routers to handle a variety of options.

Koa不稳定，仍处于活跃的开发完善阶段。使用ES6还是有点太超前了，例如只有0.11.9+的Node.js版本才能运行Koa，而现在最新的Node.js稳定版本是0.10.33。和Express一样有好也有坏的一点就是，在多种中间件的选择还是自己写中间件。就像我们之前所用的router那样，有太多类似的router中间件可供我们选择。

5.3 Hapi

5.3.1 The Good

Hapi is proud to say that their framework is based on configuration over code, and a lot of developers would argue that this is a good thing. This is very usual in large teams to add consistency and reusability. Also with the framework being backed by WalmartLabs as well as many other big name companies using Hapi in production, it has been battle tested and companies are confident enough to run their applications off of it. So all signs point towards this project continuing to mature in to a great framework.

Hapi自豪地宣称它自己是基于配置优于编码的概念，并且很多开发者认为这是一件好事。在团队项目开发中，可以很容易地增强一致性和可复用性。作为有着大名鼎鼎的WalmartLabs支持的框架和其他响当当的企业在实际生产中使用Hapi，它已经经过了实际战场的洗礼，企业们可以没有担忧地基于Hopi运行自己的应用程序。所有的迹象都表明Hapi向着成为的伟大的框架的方向持续成熟。

5.3.2 The Bad

Hapi definitely seems to be more tailored towards bigger or more complex applications. It is probably a little too much boilerplate code to throw together a simple web app and there is also a lot less examples or open source applications that use hapi. So choosing it might involve a little more part on the developer rather than using third party middleware.

Hapi绝逼适合用来开发更大更复杂的应用。但对于一个简单的web app来说，它的可能有点儿堆砌太多样板代码了。而且Hapi的可供参考样例太少了，或者说开源的使用Hapi的应用程序太少了。所以选择它对开发者的要求更高一点，而不是所使用的中间件。

6 Summary

We have seen some good but practical examples of all three frameworks. Express is definitely the most popular and most recognized framework of the three. It is almost a reaction to first create a server using Express when starting new development on an application but hopefully now there might be some thought involved whether to use Koa or Hapi as an alternative. Koa shows real promise for the future and is ahead of the pack with embracing ES6 and the web component ideology that the web development community is moving towards. Hapi should be the first consideration for large teams and large projects. It pushes for configuration over code which almost always benefits teams and the re-usability most teams strive towards. Now go out and try a new framework, maybe you’ll love it, maybe you’ll hate, but you will never know and in the end, it will make you a better developer.

我们已经看过三个框架一些棒棒的而且很实际的例子了。Express毫无疑问是三个当中最流行和最出名的框架。当你要开发一个新的应用程序的时候，使用Express来构建一个服务器可能已经成为了你的条件反射了；但希望现在你在做选择的时候会多一些思考，可以考虑选择Koa或者Hapi。Koa通过超前拥抱ES6和Web component的思想，显示了Web开发社区正在进步的对未来的承诺。对于比较大的团队和比较大的项目来说，Hapi应该成为首要选择。它所推崇的配置优于编码，对团队和对团队一直追求的可复用性都大有裨益。现在赶紧行动起来尝试使用一个新的框架，可能你会喜欢或者讨厌它，但没到最后你总不会知道结果是怎么样的，有一点无容置疑的是，它会让你成为一个更好的开发者。