MEAN全栈开发实战指南

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"MEAN Machine 是一本面向初学者的实践指南，旨在介绍JavaScript全栈开发，包括MongoDB、Express、AngularJS和Node.js（统称MEAN）。作者Chris Sevilleja和Holly Lloyd通过轻量级工具和迭代过程，让读者在实践中学习和反馈，以达到掌握MEAN栈的目的。此书于2015年3月10日发布，可在Leanpub购买。" MEAN Machine是关于JavaScript全栈开发的一本入门书籍，特别适合对MEAN技术栈感兴趣的初学者。MEAN代表MongoDB、Express、AngularJS和Node.js，这是一个基于JavaScript的开源开发工具集合，允许开发者使用同一种语言从前端到后端进行开发，从而提高效率和协同性。 1. **MongoDB**：是一个NoSQL数据库，使用JSON格式存储数据，具有灵活的数据模型和高扩展性，适合处理大量非结构化数据。 2. **Express**：是Node.js的一个框架，用于构建Web应用和服务。它提供了一套简洁的API，简化了HTTP服务器的创建和路由管理。 3. **AngularJS**：是由Google维护的前端JavaScript框架，用于构建动态单页应用程序（SPA）。它提供了数据绑定、依赖注入和模块化等功能，使前端开发更为高效。 4. **Node.js**：基于Chrome V8引擎的JavaScript运行环境，让开发者可以在服务器端使用JavaScript。它的异步、事件驱动的特性使其在处理I/O密集型任务时表现出色。为什么选择MEAN栈？ - **全栈JavaScript**：使用同一语言进行前后端开发，降低了学习曲线，提高了开发效率。 - **社区支持**：MEAN组件都有庞大的开发者社区，提供丰富的插件和解决方案。 - **快速开发**：Node.js的异步I/O和Express的简洁API使得开发快速响应的应用变得简单。 - **可扩展性**：MongoDB和Node.js都设计为可水平扩展，适合构建大型、高并发的Web应用。何时使用MEAN栈？ - **初创项目**：对于快速原型和迭代的项目，MEAN栈的灵活性和高效性很适用。 - **小团队**：由于JavaScript的普及，找到熟悉MEAN的开发者相对容易。 - **需要高度定制的Web应用**：MEAN栈允许高度定制和灵活的架构设计。本书将引导读者理解MEAN栈的各个部分，通过实例和实践帮助他们掌握这些技术。作者鼓励读者在阅读过程中积极反馈，以便不断优化和改进内容。如果你希望通过实践学习Node.js和AngularJS，那么这本书将是一个很好的起点。

Primers 9

Nginx, etc.) running with the server-side scripting language (PHP, Perl, Python) to create a dynamic

website. The server-side code is used to create the application environment by extracting data from

the database (MYSQL) and is then interpreted by the web server to produce the web page.

When a new connection is requested, Apache creates a new thread or process to handle that request,

which makes it multithreaded. Often you will have a number of idle child processes standing by

waiting to be assigned to a new request. If you configure your server to only have 50 idle processes

and 100 requests come in, some users may experience a connection timeout until some of those

processes are freed up. Of course there are several ways to handle this scalability more efficiently,

but in general Apache will use one thread per request, so to support more and more users you will

eventually need more and more servers.

Multithreading A programming model where the flow of the program has multiple

threads of control. Different parts of the program (threads) will be able to execute

simultaneously and independently, rather than waiting for each event to finish. This

is nice for the user who now doesn’t have to wait for every event to finish before they

get to see some action, but new threads require more memory, so this performance

comes with a memory trade-off.

—

This is where Node.js shines. Node is an event driven language that plays the same role as Apache.

It will interpret the client-side code to produce the web page. They are similar in that each new

connection fires a new event, but the main distinction comes from the fact that Node is asynchronous

and single threaded. Instead of using multiple threads that sit around waiting for a function or

event to finish executing, Node uses only one thread to handle all requests. Although this may seem

inefficient at first glance, it actually works out well given the asynchronous nature of Node.

Event Driven Programming The flow of a program is driven by specific events

(mouse clicks, incoming messages, key presses, etc). Most GUIs are event based and

this programming technique can be implemented in any language. —

Asynchronous Programming Asynchronous events are executed independently of the

main program’s “flow”. Rather than doing nothing while waiting for an event to occur,

the program will pass an event to the event handler queue and continue with the main

program flow. Once the event is ready, the program will return to it with a callback,

execute the code, and then return to the main flow of the program. Because of this, an

asynchronous program will most likely not run in the normal top to bottom order that

you see with synchronous code. —

Primers 10

Say, for example, a database query request comes in. Depending on how large the query is, it could

take a couple of seconds to return anything. Since there is only one thread, it may seem that nothing

else would be able to process while the query is executing. This would of course result in slow load

times for your users which could be detrimental to the success of your site. Fortunately Node handles

multiple requests much more gracefully than that by using callbacks.

Asynchronous Callbacks A function that is passed as an argument to be executed at a

later time (when it is ready). Callbacks are used when a function may need more time

to execute in order to return the correct return values. —

There are two types of callbacks: synchronous and asynchronous. Synchronous callbacks are

considered “blocking” callbacks, meaning that your program will not continue running until

the callback function is finished executing. Because I/O operations take a great deal of time to

execute, this may make your application appear to be slow or even frozen to users. Node’s use

of asynchronous callbacks (also known as non-blocking callbacks) allow your program to continue

executing while I/O operations are taking place. Once the operations are complete, they will issue

an interrupt/callback to tell your program that its ready to execute. Once the function is complete,

your program will return back to what it was doing. Of course having several callbacks throughout

your code can get very chaotic very fast, so it’s up to you, the programmer, to make sure that you

do it correctly.

NPM and Packages

One of the benefits of Node is its package manager, npm¹⁷. Like Ruby has RubyGems and PHP

has Composer, Node has npm. npm comes bundled with Node and will let us pull in a number of

packages to fulfill our needs.

Packages can extend functionality in Node and this package system is one thing that makes Node so

powerful. The ability to have a set of code that you can reuse across all your projects is incredible

and makes development that much easier.

Multiple packages can be brought together and intertwined to create a number of complex

applications.

Listed below are a few of the many popular packages¹⁸ that are used in Node:

• ExpressJS¹⁹ is currently the most starred package on npm’s site²⁰ (we’ll use this in the book of

course)

¹⁷https://www.npmjs.org/

¹⁸https://www.npmjs.org/browse/star

¹⁹http://expressjs.com/

²⁰https://www.npmjs.org/browse/star

Primers 11

• Mongoose²¹ is the package we will use to interact with MongoDB.

• GruntJS²² for automating tasks (we’ll use this later in the book)

• PassportJS²³ for authentication with many social services.

• Socket.io²⁴ for building real time websocket applications (we’ll use this later in the book)

• Elasticsearch²⁵ for providing high scalability search operations.

Frameworks

There are several Node frameworks in existence. We’re using Express in this book, but the concepts

taught here will easily transfer over to other popular frameworks.

The other main frameworks of interest are:

• HapiJS²⁶ - Great framework being used by more and more enterprise companies.

• KoaJS²⁷ - A fork of Express

• Restify²⁸ - Borrows from Express syntax to create a framework devoted to building REST APIs

• Sails²⁹ - Framework built to emulate the MVC model

Express will handle nearly all of the tasks that you need and it is extremely robust, usable, and now

has commercial backing as it was recently bought/sponsored by StrongLoop³⁰.

While those other frameworks are great in their own rights (definitely take a look at them), we will

be focusing on Express. It is the MEAN stack after all.

ExpressJS

Express is a lightweight platform for building web apps using NodeJS. It helps organize web apps

on the server side. The ExpressJS website³¹ describes Express as “a minimal and flexible node.js web

application framework”.

Express hides a lot of the inner workings of Node, which allows you to dive into your application

code and get things up and running a lot faster. It’s fairly easy to learn and still gives you a bit of

flexibility with its structure. There is a reason it is currently the most popular framework for Node.

Some of the big names using Express are:

²¹http://mongoosejs.com/

²²http://gruntjs.com/

²³http://passportjs.org/

²⁴http://socket.io/

²⁵http://www.elasticsearch.com/

²⁶http://hapijs.com/

²⁷http://koajs.com/

²⁸http://mcavage.me/node-restify/

²⁹http://sailsjs.org/#/

³⁰http://strongloop.com/strongblog/tj-holowaychuk-sponsorship-of-express/

³¹http://expressjs.com

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MEAN全栈开发实战指南

mean-machine-sandbox:Mean Machine项目的沙箱

mean-machine

k-means mean shift

train_loss.append(mean_loss/len(trainloader))

tell me about the measurement of models in machine learning

生成mean shift图像分割的matlab程序

UserWarning: When training, we now always track global mean and variance.

Bayesian Reasoning and Machine Learning第二章代码

K-meanPython

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