NODE HERO

Oct 16, 2019 | Publisher: edocr | Category: Technology |  | Collection: Business Ideas | Views: 49 | Likes: 2

RisingStack 1 NODE HERO Get started with Node.js and deliver software products using it. From the Engineers of RisingStack 2 GETTING STARTED WITH NODE.JS 03 Table of contents USING NPM 08 UNDERSTANDING ASYNC PROGRAMMING 12 USING DATABASES 22 THE REQUEST MODULE 28 PROJECT STRUCTURING 32 AUTHENTICATION USING PASSPORT.JS 35 UNIT TESTING 40 DEBUGGING 46 YOUR FIRST NODE.JS SERVER 17 SECURITY 50 DEPLOYING YOUR APPLICATION 55 MONITORING NODE.JS APPLICATIONS 60 RisingStack 3 GETTING STARTED WITH NODE.JS We are going to start with the basics - no prior Node.js knowledge is needed. The goal of this book is to get you started with Node.js and make sure you understand how to write an application using it. In this very first chapter, you will learn what Node.js is, how to install it on your computer and how to get started with it - so in the next ones we can do actual development. Let's get started! Node.js in a Nutshell The official Node.js logo Node.js is a JavaScript runtime built on Chrome's V8 JavaScript engine. Node.js uses an event-driven, non-blocking I/O model that makes it lightweight and efficient. In other words: Node.js offers you the possibility to write servers using JavaScript with an incredible performance. As the official statement says: Node.js is a runtime that uses the same V8 Javascript engine you can find in the Google Chrome browser. But that wouldn't be enough for Node.js's success - Node.js utilizes libuv, a multi-platform support library with a focus on asynchronous I/O. The official libuv logo From a developer's point of view Node.js is single-threaded - but under the hood libuv handles threading, file system events, implements the event loop, features thread pooling and so on. In most cases you won't interact with it directly. Installing Node.js to get started To get the latest Node.js binary you can visit the official Node.js website: https://nodejs.org/en/download/. RisingStack 4 With this approach it is quite easy to get started - however if later down the road you want to add more Node.js versions, it is better to start using nvm, the Node Version Manager. Once you install it, you can use a very simple CLI API that you can interact with: Installing Node.js Versions Then, if you want to check out the experimental version: To verify that you have Node.js up and running, run this: If everything is ok, it will return the version number of the currently active Node.js binary. Using Node.js Versions If you are working on a project supporting Node.js v4, you can start using it with the following command: Then you can switch to Node.js v5 with the very same command: Okay, now we know how to install and switch between Node.js versions - but what's the point? Since the Node.js Foundation was formed, Node.js has a release plan. It's quite similar to the other projects of the Linux Foundation. This means that there are two releases: the stable release and the experimental one. In Node.js the stable versions with long-term support (LTS) are the ones starting with even numbers (4, 6, 8 ...) and the experimental version are the odd numbers (5, 7 ...). We recommend you to use the LTS version in production and try out new things with the experimental one. If you are on Windows, there is an alternative for nvm: nvm-windows. nvm install 4.4 nvm install 5 node --version nvm use 4 nvm use 5 RisingStack 5 Hello World To get started with Node.js, let's try it in the terminal! Start Node.js by simply typing node: Okay, let's try printing something: Once you hit Enter, you will get something like this: Feel free to play with Node.js by using this interface - I usually try out small snippets here if I don't want to put them into a file. It is time to create our Hello Node.js application! Let's start with creating a file called index.js. Open up your IDE (Atom, Sublime, Code - you name it), create a new file and save it with the name index.js. If you're done with that, copy the following snippet into this file: To run this file, you should open up your terminal again and navigate to the directory in which you placed index.js. Once you successfully navigated yourself to the right spot, run your file using thenode index.js command. You can see that it will produce the same output as before - printing the string directly into the terminal. Modularization of Your Application Now you have your index.js file, so it is time to level up your game! Let's create something more complex by splitting our source code into multiple JavaScript files with the purpose of readability and maintainability. To get started, head back to your IDE (Atom, Sublime, $ node > $ node > console.log('hello from Node.js') > console.log('hello from Node.js') hello from Node.js undefined // index.js console.log('hello from Node.js') RisingStack 6 Code - you name it) and create the following directory structure (with empty files), but leave the package.json out for now, we will generate it automatically in the next step: Every Node.js project starts with creating a package.json file - you can think of it as a JSON representation of the application and its' dependencies. It contains your application's name, the author (you), and all the dependencies that is needed to run the application. We are going to cover the dependencies section later in the Using NPM chapter of Node Hero. You can interactively generate your package.json file using the npm init command in the terminal. After hitting enter you will asked to give several inputs, like the name of your application, version, description and so on. No need to worry, just hit enter until you get the JSON snippet and the question is it ok?. Hit enter one last time and viola, your package.json has been automatically generated and placed in the folder of your application. If you open that file in your IDE, it will look very similar to the code snippet below. It's a good practice to add a start script to your package.json - once you do that as shown in the example above you can start your application with the npm start command as well. It comes really handy when you want to deploy your application to a PaaS provider - they can recognize it and start your application using that. Now let's head back to the first file you created called index.js. I recommend to keep the this file very thin - only requiring the application itself (the index.js file from the /app subdirectory you created before). Copy the following script into your index.js file and hit save to do this: // index.js require('./app/index') app | calc.js | index.js index.js package.json // package.json { "name": "@risingstack/node-hero", "version": "1.0.0", "description": "", "main": "index.js", "scripts": { "test": "echo \"Error: no test specified\" && exit 1", "start": "node index.js" }, "author": "", "license": "ISC" } RisingStack 7 Now it is time to start building the actual application. Open the index. js file from the /app folder to create a very simple example: adding an array of numbers. In this case the index.js file will only contain the numbers we want to add, and the logic that does the calculation needs to be placed in a separate module. Paste this script to the index.js file in your /app directory. Now paste the actual business logic into the calc.js file that can be found in the same folder. To check if you'd succeeded, save these files, open up terminal and enter npm start or node index.js. If you did everything right, you will get back the answer: 19. If something went wrong, review the console log carefully and find the issue based on that. In our next chapter called Using NPM we are going to take a look on how to use NPM, the package manager for JavaScript. // app/calc.js function sum (arr) { return arr.reduce(function(a, b) { return a + b }, 0) } module.exports.sum = sum // app/index.js const calc = require('./calc') const numbersToAdd = [ 3, 4, 10, 2 ] const result = calc.sum(numbersToAdd) console.log(`The result is: ${result}`) RisingStack 8 USING NPM In this chapter, you'll learn what NPM is and how to use it. Let's get started! NPM in a Nutshell NPM is the package manager used by Node.js applications - you can find a ton of modules here, so you don't have to reinvent the wheel. It is like Maven for Java or Composer for PHP. There are two primary interfaces you will interact with - the NPM website and the NPM command line toolkit. Both the website and the CLI uses the same registry to show modules and search for them. The Website The NPM website can be found at https://npmjs.com. Here you can sign up as a new user or search for packages. The Command Line Interface To run the CLI you can run it simply with: npm Note, that NPM is bundled with the Node.js binary, so you don't have to install it - however, if you want to use a specific npm version, you can update it. If you want to install npm version 3, you can do that with: npm install npm@3 -g. RisingStack 9 Using NPM: Tutorial You have already met NPM in the previous chapter, when you created the package.json file. Let's extend that knowledge! Adding Dependencies In this section you are going to learn how to add runtime dependencies to your application. Once you have your package.json file you can add dependencies to your application. Let's add one! Try the following: With this single command we achieved two things: first of all, lodash is downloaded and placed into the node_modules folder. This is the folder where all your external dependencies will be put. Usually, you don't want to add this folder to your source control, so if you are using git make sure to add it to the .gitignore file. This can be a good starting point for your .gitignore [Click here for the GitHub link] Let's take a look at what happened in the package.json file! A new property called dependencies have appeared: This means that lodash with version 4.6.1 is now installed and ready to be used. Note, that NPM follows SemVer to version packages. Given a version number MAJOR.MINOR.PATCH, increment the MAJOR version when you make incompatible API changes, MINOR version when you add functionality in a backwards-compatible manner, and PATCH version when you make backwards-compatible bug fixes. For more information: http://semver.org/ As lodash is ready to be used, let's see how we can do so! You can npm install lodash --save "dependencies": { "lodash": "4.6.1" } RisingStack 10 do it in the same way you did it with your own module except now you don't have to define the path, only the name of the module: Adding Development Dependencies In this section you are going to learn how to add build-time dependencies to your application. When you are building web applications, you may need to minify your JavaScript files, concatenating CSS files and so on. The modules that will do it will be only ran during the building of the assets, so the running application doesn't need them. You can install such scripts with: Once you do that, a new section will appear in your package.json file called devDependencies . All the modules you install with --save-dev will be placed there - also, they will be put in the very same node_modules directory. NPM Scripts NPM script is a very powerful concept - with the help of them you can build small utilities or even compose complex build systems. The most common ones are the start and the test scripts. With the start you can define how one should start your application, while test is for running tests. In your package.json they can look something like this: // index.js const _ = require('lodash') _.assign({ 'a': 1 }, { 'b': 2 }, { 'c': 3 }); // { 'a': 1, 'b': 2, 'c': 3 } npm install mocha --save-dev "scripts": { "start": "node index.js", "test": "mocha test", "your-custom-script": "echo npm" } RisingStack 11 Things to notice here: start: pretty straightforward, it just describes the starting point of your application, it can be invoked with npm start test: the purpose of this one is to run your tests - one gotcha here is that in this case mocha doesn't need to be installed globally, as npm will look for it in the node_modules/.bin folder, and mocha will be placed there as well. It can be invoked with: npm test. your-custom-script: anything that you want, you can pick any name. It can be invoked with npm run your-custom-script - don't forget the run part! Scoped / Private Packages Originally NPM had a global shared namespace for module names - with more than 250.000 modules in the registry most of the simple names are already taken. Also, the global namespace contains public modules only. NPM addressed this problem with the introduction of scoped packages. Scoped packages has the following naming pattern: You can install scoped packages the same way as you did before: It will show up in your package.json in the following way: Requiring scoped packages works as expected: For more information refer to the NPM scoped module docs. In the next chapter, you can learn the principles of async programming using callbacks and Promises. @myorg/mypackage npm install @myorg/mypackage --save-dev "dependencies": { "@myorg/mypackage": "^1.0.0" } npm install @myorg/mypackage --save-dev RisingStack 12 UNDERSTANDING ASYNC PROGRAMMING In this chapter, I'll guide you through async programming principles, and show you how to do async in JavaScript and Node.js. Synchronous Programming In traditional programming practice, most I/O operations happen synchronously. If you think about Java, and about how you would read a file using Java, you would end up with something like thiS: try(FileInputStream inputStream = new FileInputStream("foo.txt")) { Session IOUtils; String fileContent = IOUtils.toString(inputStream); } What happens in the background? The main thread will be blocked until the file is read, which means that nothing else can be done in the meantime. To solve this problem and utilize your CPU better, you would have to manage threads manually. If you have more blocking operations, the event queue gets even worse: (The red bars show when the process is waiting for an external resource's response and is blocked, the black bars show when your code is running, the green bars show the rest of the application) To resolve this issue, Node.js introduced an asynchronous programming model. RisingStack 13 Asynchronous programming in Node.js Asynchronous I/O is a form of input/output processing that permits other processing to continue before the transmission has finished. In the following example, I will show you a simple file reading process in Node.js - both in a synchronous and asynchronous way, with the intention of show you what can be achieved by avoiding blocking your applications. Let's start with a simple example - reading a file using Node.js in a synchronous way: const fs = require('fs') let content try { content = fs.readFileSync('file.md', 'utf-8') } catch (ex) { console.log(ex) } console.log(content) What did just happen here? We tried to read a file using the synchronous interface of the fs module. It works as expected - the content variable will contain the content of file.md. The problem with this approach is that Node.js will be blocked until the operation is finished - meaning it can do absolutely nothing while the file is being read. Let's see how we can fix it! Asynchronous programming - as we know now in JavaScript - can only be achieved with functions being first-class citizens of the language: they can be passed around like any other variables to other functions. Functions that can take other functions as arguments are called higher-order functions. One of the easiest example for higher order functions: const numbers = [2,4,1,5,4] function isBiggerThanTwo (num) { return num > 2 } numbers.filter(isBiggerThanTwo) In the example above we pass in a function to the filter function. This way we can define the filtering logic. RisingStack 14 This is how callbacks were born: if you pass a function to another function as a parameter, you can call it within the function when you are finished with your job. No need to return values, only calling another function with the values. These so-called error-first callbacks are in the heart of Node.js itself - the core modules are using it as well as most of the modules found on NPM. Things to notice here: error-handling: instead of a try-catch block you have to check for errors in the callback no return value: async functions don't return values, but values will be passed to the callbacks Let's modify this file a little bit to see how it works in practice: The output of this script will be: As you can see once we started to read our file the execution continued, and the application printed end of the file. Our callback was only called once the file read was finished. How is it possible? Meet the event loop. const fs = require('fs') console.log('start reading a file...') fs.readFile('file.md', 'utf-8', function (err, content) { if (err) { console.log('error happened during reading the file') return console.log(err) } console.log(content) }) console.log('end of the file') start reading a file... end of the file error happened during reading the file const fs = require('fs') fs.readFile('file.md', 'utf-8', function (err, content) { if (err) { return console.log(err) } console.log(content) }) RisingStack 15 The Event Loop The event loop is in the heart of Node.js / Javascript - it is responsible for scheduling asynchronous operations. Before diving deeper, let's make sure we understand what event-driven programming is. Event-driven programming is a programming paradigm in which the flow of the program is determined by events such as user actions (mouse clicks, key presses), sensor outputs, or messages from other programs/threads. In practice, it means that applications act on events. Also, as we have already learned in the first chapter, Node.js is single- threaded - from a developer's point of view. It means that you don't have to deal with threads and synchronizing them, Node.js abstracts this complexity away. Everything except your code is executing in parallel. To understand the event loop more in-depth, continue watching this video: Async Control Flow As now you have a basic understanding of how async programming works in JavaScript, let's take a look at a few examples on how you can organize your code. RisingStack 16 Async.js To avoid the so-called Callback-Hell one thing you can do is to start using async.js. Async.js helps to structure your applications and makes control flow easier. Let's check a short example of using Async.js, and then rewrite it by using Promises. The following snippet maps through three files for stats on them: Promises The Promise object is used for deferred and asynchronous computations. A Promise represents an operation that hasn't completed yet but is expected in the future. In practice, the previous example could be rewritten as follows: Of course, if you use a method that has a Promise interface, then the Promise example can be a lot less in line count as well. In the next chapter, you will learn how to fire up your first Node.js HTTP server. function stats (file) { return new Promise((resolve, reject) => { fs.stat(file, (err, data) => { if (err) { return reject (err) } resolve(data) }) }) } Promise.all([ stats('file1'), stats('file2'), stats('file3') ]) .then((data) => console.log(data)) .catch((err) => console.log(err)) async.parallel(['file1', 'file2', 'file3'], fs.stat, function (err, results) { // results is now an array of stats for each file }) RisingStack 17 YOUR FIRST NODE.JS SERVER In this chapter, I'll guide you how you can fire up a simple Node.js HTTP server and start serving requests. The http module for your Node.js server When you start building HTTP-based applications in Node.js, the built- in http/https modules are the ones you will interact with. Now, let's create your first Node.js HTTP server! We'll need to require the http module and bind our server to the port 3000 to listen on. // content of index.js const http = require('http') const port = 3000 const requestHandler = (request, response) => { console.log(request.url) response.end('Hello Node.js Server!') } const server = http.createServer(requestHandler) server.listen(port, (err) => { if (err) { return console.log('something bad happened', err) } console.log(`server is listening on ${port}`) }) You can start it with: Things to notice here: requestHandler : this function will be invoked every time a request hits the server. If you visit localhost:3000 from your browser, two log messages will appear: one for / and one for favicon.ico if (err): error handling - if the port is already taken, or for any other reason our server cannot start, we get notified here The http module is very low-level - creating a complex web application using the snippet above is very time-consuming. This is the reason why we usually pick a framework to work with for our projects. There are a lot you can pick from, but these are the most popular ones: express hapi koa restify For this and the next chapters we are going to use Express, as you will find the most modules on NPM for Express. $ node index.js RisingStack 18 Express Fast, unopinionated, minimalist web framework for Node.js - http:// expressjs.com/ Adding Express to your project is only an NPM install away: Once you have Express installed, let's see how you can create a similar application as before: const express = require('express') const app = express() const port = 3000 app.get('/', (request, response) => { response.send('Hello from Express!') }) app.listen(port, (err) => { if (err) { return console.log('something bad happened', err) } console.log(`server is listening on ${port}`) }) The biggest difference what you have to notice here is that Express by default gives you a router. You don't have to check manually for the URL to decide what to do, but instead, you define the application's routing with app.get, app.post, app.put, etc. They are translated to the corresponding HTTP verbs. One of the most powerful concepts that Express implements is the middleware pattern. Middlewares You can think of middlewares as Unix pipelines, but for HTTP requests. In the diagram you can see how a request can go through an Express application. It travels to three middlewares. Each can modify it, then based on the business logic either the third middleware can send back a response or it can be a route handler. $ npm install express --save RisingStack 19 In practice, you can do it this way: const express = require('express') const app = express() app.use((request, response, next) => { console.log(request.headers) next() }) app.use((request, response, next) => { request.chance = Math.random() next() }) app.get('/', (request, response) => { response.json({ chance: request.chance }) }) app.listen(3000) Things to notice here: app.use : this is how you can define middlewares - it takes a function with three parameters, the first being the request, the second the response and the third one is the next callback. Calling next signals Express that it can jump to the next middleware or route handler. The first middleware just logs the headers and instantly calls the next one. The seconds one adds an extra property to it - this is one of the most powerful features of the middleware pattern. Your middlewares can append extra data to the request object that downstream middlewares can read/alter. Error handling As in all frameworks, getting the error handling right is crucial. In Express you have to create a special middleware function to do so - a middleware with four parameters: const express = require('express') const app = express() app.get('/', (request, response) => { throw new Error('oops') }) app.use((err, request, response, next) => { // log the error, for now just console.log console.log(err) response.status(500).send('Something broke!') }) RisingStack 20 Things to notice here: The error handler function should be the last function added with app.use. The error handler has a next callback - it can be used to chain multiple error handlers. Rendering HTML So far we have taken a look on how to send JSON responses - it is time to learn how to render HTML the easy way. For that, we are going to use the handlebars package with the express-handlebars wrapper. First, let's create the following directory structure: Once you have that, populate index.js with the following snippet: The code above initializes the handlebars engine and sets the layouts directory to views/layouts. This is the directory where your layouts will be stored. Once you have this setup, you can put your initial html into the main.hbs - to keep things simple let's go with this one: Express handlebars {{{body}}} You can notice the {{{body}}} placeholder - this is where your content will be placed - let's create the home.hbs! Hello {{name}} index.js views home.hbs layouts main.hbs // index.js const path = require('path') const express = require('express') const exphbs = require('express-handlebars') app.engine('.hbs', exphbs({ defaultLayout: 'main', extname: '.hbs', layoutsDir: path.join(__dirname, 'views/layouts') })) app.set('view engine', '.hbs') app.set('views', path.join(__dirname, 'views')) RisingStack 21 The last thing we have to do to make it work is to add a route handler to our Express application: The render method takes two parameters: The first one is the name of the view, and the second is the data you want to render. Once you call that endpoint you will end up with something like this: Express handlebars Hello John This is just the tip of the iceberg - to learn how to add more layouts and even partials, please refer to the official express-handlebars documentation. Debugging Express In some cases, you may need to see what happens with Express when your application is running. To do so, you can pass the following environment variable to Express: DEBUG=express*. You have to start your Node.js HTTP server using: Summary This is how can you set up your first Node.js HTTP server from scratch. I recommend Express to begin with, then feel free to experiment. Let me know how did it go in the comments. In the next chapter, you will learn how to retrieve information from databases. app.get('/', (request, response) => { response.render('home', { name: 'John' }) }) $ DEBUG=express* node index.js RisingStack 22 USING DATABASES In the following Node.js database chapter, I'll show you how you can set up a Node.js application with a database, and teach you the basics of using it. Storing data in a global variable Serving static pages for users - as you have learned it in the previous chapter - can be suitable for landing pages, or for personal blogs. However, if you want to deliver personalized content you have to store the data somewhere. Let's take a simple example: user signup. You can serve customized content for individual users or make it available for them after identification only. If a user wants to sign up for your application, you might want to create a route handler to make it possible: const users = [] app.post('/users', function (req, res) { // retrieve user posted data from the body const user = req.body users.push({ name: user.name, age: user.age }) res.send('successfully registered') }) This way you can store the users in a global variable, which will reside in memory for the lifetime of your application. Using this method might be problematic for several reasons: RAM is expensive, memory resets each time you restart your application, if you don't clean up, sometimes you'll end up with stack overflow. Storing data in a file The next thing that might come up in your mind is to store the data in files. If we store our user data permanently on the file system, we can avoid the previously listed problems. RisingStack 23 This method looks like the following in practice: This way we won't lose user data, not even after a server reset. This solution is also cost efficient, since buying storage is cheaper than buying RAM. Unfortunately storing user data this way still has a couple of flaws: Appending is okay, but think about updating or deleting. If we're working with files, there is no easy way to access them in parallel (system-wide locks will prevent you from writing). When we try to scale our application up, we cannot split files (you can, but it is way beyond the level of this tutorial) in between servers. This is where real databases come into play. You might have already heard that there are two main kinds of databases: SQL and NoSQL. SQL Let's start with SQL. It is a query language designed to work with relational databases. SQL has a couple of flavors depending on the product you're using, but the fundamentals are same in each of them. The data itself will be stored in tables, and each inserted piece will be represented as a row in the table, just like in Google Sheets, or Microsoft Excel. Within an SQL database, you can define schemas - these schemas will provide a skeleton for the data you'll put in there. The types of the different values have to be set before you can store your data. For example, you'll have to define a table for your user data, and have to tell the database that it has a username which is a string, and age, which is an integer type. const fs = require('fs') app.post('/users', function (req, res) { const user = req.body fs.appendToFile('users.txt', JSON.stringify({ name: user.name, age: user.age }), (err) => { res.send('successfully registered') }) }) RisingStack 24 NoSQL On the other hand, NoSQL databases have become quite popular in the last decade. With NoSQL you don't have to define a schema and you can store any arbitrary JSON. This is handy with JavaScript because we can turn any object into a JSON pretty easily. Be careful, because you can never guarantee that the data is consistent, and you can never know what is in the database. Node.js and MongoDB There is a common misconception with Node.js what we hear all the time: "Node.js can only be used with MongoDB (which is the most popular NoSQL database)." According to my experience, this is not true. There are drivers available for most of the databases, and they also have libraries on NPM. In my opinion, they are as straightforward and easy to use as MongoDB. Node.js and PostgreSQL For the sake of simplicity, we're going to use SQL in the following example. My dialect of choice is PostgreSQL. To have PostgreSQL up and running you have to install it on your computer. If you're on a Mac, you can use homebrew to install PostgreSQL. Otherwise, if you're on Linux, you can install it with your package manager of choice. For further information read this excellent guide on getting your first database up and running. RisingStack 25 If you're planning to use a database browser tool, I'd recommend the command line program called psql - it's bundled with the PostgreSQL server installation. Here's a small cheat sheet that will come handy if you start using it. If you don't like the command-line interface, you can use pgAdmin which is an open source GUI tool for PostgreSQL administration. Note that SQL is a language on its own, we won't cover all of its features, just the simpler ones. To learn more, there are a lot of great courses online that cover all the basics on PostgreSQL. Node.js Database Interaction First, we have to create the database we are going to use. To do so, enter the following command in the terminal: createdb node_hero Then we have to create the table for our users. Finally, we can get back to coding. Here is how you can interact with your database via your Node.js program. This was just a simple example, a 'hello world' in PostgreSQL. Notice that the first parameter is a string which is our SQL command, the second parameter is an array of values that we'd like to parameterize our query with. CREATE TABLE users( name VARCHAR(20), age SMALLINT ); 'use strict' const pg = require('pg') const conString = 'postgres://username:password@ localhost/node_hero' // make sure to match your own database's credentials pg.connect(conString, function (err, client, done) { if (err) { return console.error('error fetching client from pool', err) } client.query('SELECT $1::varchar AS my_first_query', ['node hero'], function (err, result) { done() if (err) { return console.error('error happened during query', err) } console.log(result.rows[0]) process.exit(0) }) }) RisingStack 26 It is a huge security error to insert user input into databases as they come in. This protects you from SQL Injection attacks, which is a kind of attack when the attacker tries to exploit severely sanitized SQL queries. Always take this into consideration when building any user facing application. To learn more, check out our Node.js Application Security checklist. Let's continue with our previous example. Achievement unlocked: the user is stored in the database! :) Now let's try retrieving them. Next, let's add a new endpoint to our application for user retrieval. app.post('/users', function (req, res, next) { const user = req.body pg.connect(conString, function (err, client, done) { if (err) { // pass the error to the express error handler return next(err) } client.query('INSERT INTO users (name, age) VALUES ($1, $2);', [user.name, user.age], function (err, result) { done() //this done callback signals the pg driver that the connection can be closed or returned to the connection pool if (err) { // pass the error to the express error handler return next(err) } res.send(200) }) }) }) app.get('/users', function (req, res, next) { pg.connect(conString, function (err, client, done) { if (err) { // pass the error to the express error handler return next(err) } client.query('SELECT name, age FROM users;', [], function (err, result) { done() if (err) { // pass the error to the express error handler return next(err) } res.json(result.rows) }) }) }) RisingStack 27 That wasn't that hard, was it? Now you can run any complex SQL query that you can come up with within your Node.js application. With this technique, you can store data persistently in your application, and thanks to the hard-working team of the node-postgres module, it is a piece of cake to do so. We have gone through all the basics you have to know about using databases with Node.js. Now go, and create something yourself. Try things out and experiment, because that's the best way of becoming a real Node Hero! Practice and be prepared for the next chapter on how to communicate with third-party APIs! RisingStack 28 THE REQUEST MODULE In the following chapter, you will learn the basics of HTTP, and how you can fetch resources from external sources using the Node.js request module. What's HTTP? HTTP stands for Hypertext Transfer Protocol. HTTP functions as a requestresponse protocol in the clientserver computing model. HTTP Status Codes Before diving into the communication with other APIs, let's review the HTTP status codes we may encounter during the process. They describe the outcome of our requests and are essential for error handling. 1xx - Informational 2xx - Success: These status codes indicate that our request was received and processed correctly. The most common success codes are 200 OK, 201 Created and 204 No Content. 3xx - Redirection: This group shows that the client had to do an additional action to complete the request. The most common redirection codes are 301 Moved Permanently , 304 Not Modified. 4xx - Client Error: This class of status codes is used when the request sent by the client was faulty in some way. The server response usually contains the explanation of the error. The most common client error codes are 400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found, 409 Conflict. 5xx - Server Error: These codes are sent when the server failed to fulfill a valid request due to some error. The cause may be a bug in the code or some temporary or permanent incapability. The most common server error codes are 500 Internal Server Error, 503 Service Unavailable. If you'd like to learn more about HTTP status codes, you can find a detailed explanation about them here. RisingStack 29 Sending Requests to External APIs Connecting to external APIs is easy in Node. You can just require the core HTTP module and start sending requests. Of course, there are much better ways to call an external endpoint. On NPM you can find multiple modules that can make this process easier for you. Fo r example, the two most popular ones are the request and superagent modules. Both of these modules have an error-first callback interface that can lead to some issues (I bet you've heard about Callback-Hell), but luckily we have access to the promise-wrapped versions. Using the Node.js Request Module Using the request-promise module is simple. After installing it from NPM, you just have to require it: Sending a GET request is as simple as: If you are calling a JSON API, you may want the request-promise to parse the response automatically. In this case, just add this to the request options: const request = require('request-promise') json: true const options = { method: 'GET', uri: 'https://risingstack.com' } request(options) .then(function (response) { // Request was successful, use the response object at will }) .catch(function (err) { // Something bad happened, handle the error }) RisingStack 30 POST requests work in a similar way: To add query string parameters you just have to add the qs property to the options object: This will make your request URL: https://risingstack.com?limit=10&skip=20&sort=asc. You can also define any header the same way we added the query parameters: Error handling Error handling is an essential part of making requests to external APIs, as we can never be sure what will happen to them. Apart from our client errors the server may respond with an error or just send data in a wrong or inconsistent format. Keep these in mind when you try handling the response. Also, using catch for every request is a good way to avoid the external service crashing our server. const options = { method: 'GET', uri: 'https://risingstack.com', qs: { limit: 10, skip: 20, sort: 'asc' } } const options = { method: 'POST', uri: 'https://risingstack.com/login', body: { foo: 'bar' }, json: true // JSON stringifies the body automatically } request(options) .then(function (response) { // Handle the response }) .catch(function (err) { // Deal with the error }) const options = { method: 'GET', uri: 'https://risingstack.com', headers: { 'User-Agent': 'Request-Promise', 'Authorization': 'Basic QWxhZGRpbjpPcGVuU2VzYW1l' } } RisingStack 31 Putting it together As you have already learned how to spin up a Node.js HTTP server, how to render HTML pages, and how to get data from external APIs, it is time to put them together! In this example, we are going to create a small Express application that can render the current weather conditions based on city names. (To get your AccuWeather API key, please visit their developer site) The example above does the following: creates an Express server sets up the handlebars structure - for the .hbs file please refer to the Node.js HTTP tutorial sends a request to the external API if everything is ok, it renders the page otherwise, it shows the error page and logs the error In the next chapter of Node Hero you are going to learn how to structure your Node.js projects correctly. const express = require('express') const rp = require('request-promise') const exphbs = require('express-handlebars') const app = express() app.engine('.hbs', exphbs({ defaultLayout: 'main', extname: '.hbs', layoutsDir: path.join(__dirname, 'views/layouts') })) app.set('view engine', '.hbs') app.set('views', path.join(__dirname, 'views')) app.get('/:city', (req, res) => { rp({ uri: 'http://apidev.accuweather.com/locations/v1/ search', qs: { q: req.params.city, apiKey: 'api-key' // Use your accuweather API key here }, json: true }) .then((data) => { res.render('index', data) }) .catch((err) => { console.log(err) res.render('error') }) }) app.listen(3000) RisingStack 32 PROJECT STRUCTURING Most Node.js frameworks don't come with a fixed directory structure and it might be challenging to get it right from the beginning. In this chapter, you will learn how to properly structure a Node.js project to avoid confusion when your applications start to grow. The 5 fundamental rules of Project Structuring There are a lot of possible ways to organize a Node.js project - and each of the known methods has their ups and downs. However, according to our experience, developers always want to achieve the same things: clean code and the possibility of adding new features with ease. In the past years at RisingStack, we had a chance to build efficient Node applications in many sizes, and we gained numerous insights regarding the dos and donts of project structuring. We have outlined five simple guiding rules which we enforce during Node.js development. If you manage to follow them, your projects will be fine: Rule 1: Organize your Files Around Features, Not Roles Imagine, that you have the following directory structure: The problems with this approach are: to understand how the product pages work, you have to open up three different directories, with lots of context switching, you end up writ ing long paths when requiring modules: require('../../controllers/user.js') Instead of this, you can structure your Node.js applications around // DON'T . controllers | product.js | user.js models | product.js | user.js views | product.hbs | user.hbs RisingStack 33 product features / pages / components. It makes understanding a lot easier: Rule 2: Don't Put Logic in index.js Files Use these files only to export functionality, like: Rule 3: Place Your Test Files Next to The Implementation Tests are not just for checking whether a module produces the expected output, they also document your modules (you will learn more on testing in the upcoming chapters). Because of this, it is easier to understand if test files are placed next to the implementation. Put your additional test files to a separate test folder to avoid confusion. // DO . product | index.js | product.js | product.hbs user | index.js | user.js | user.hbs // product/index.js var product = require('./product') module.exports = { create: product.create } . test | setup.spec.js product | index.js | product.js | product.spec.js | product.hbs user | index.js | user.js | user.spec.js | user.hbs RisingStack 34 Rule 4: Use a config Directory To place your configuration files, use a config directory. Rule 5: Put Your Long npm Scripts in a scripts Directory Create a separate directory for your additional long scripts in package.json In the next chapter of Node Hero, you are going to learn how to authenticate users using Passport.js. . scripts | syncDb.sh | provision.sh product | index.js | product.js | product.spec.js | product.hbs . config | index.js | server.js product | index.js | product.js | product.spec.js | product.hbs RisingStack 35 NODE.JS AUTHENTICATION USING PASSPORT.JS In this chapter, you are going to learn how to implement a local Node. js authentication strategy using Passport.js and Redis. Technologies to use Before jumping into the actual coding, let's take a look at the new technologies we are going to use in this chapter. What is Passport.js? Simple, unobtrusive authentication for Node.js - passportjs.org Passport is an authentication middleware for Node.js which we are going to use for session management. What is Redis? Redis is an open source (BSD licensed), in-memory data structure store, used as database, cache and message broker. - redis.io We are going to store our user's session information in Redis, and not in the process's memory. This way our application will be a lot easier to scale. The Demo Application For demonstration purposes, let's build an application that does only the following: exposes a login form, exposes two protected pages: a profile page, secured notes RisingStack 36 The Project Structure You have already learned how to structure Node.js projects in the previous chapter of Node Hero, so let's use that knowledge! We are going to use the following structure: As you can see we will organize files and directories around features. We will have a user page, a note page, and some authentication related functionality. (Download the full source code at https://github.com/RisingStack/ nodehero-authentication) The Node.js Authentication Flow Our goal is to implement the following authentication flow into our application: 1. User enters username and password 2. The application checks if they are matching 3. If they are matching, it sends a Set-Cookie header that will be used to authenticate further pages 4. When the user visits pages from the same domain, the previously set cookie will be added to all the requests 5. Authenticate restricted pages with this cookie To set up an authentication strategy like this, follow these three steps: 1. Set up Express 2. Set up Passport for Node.js 3. Add Protected Endpoints app | authentication | note | user | index.js | layout.hbs config | index.js index.js package.json RisingStack 37 Step 1: Setting up Express We are going to use Express for the server framework - you can learn more on the topic by reading our Express tutorial. What did we do here? First of all, we required all the dependencies that the session management needs. After that we have created a new instance from the express-session module, which will store our sessions. For the backing store, we are using Redis, but you can use any other, like MySQL or MongoDB. Step 2: Setting up Passport for Node.js Passport is a great example of a library using plugins. For this tutorial, we are adding the passport-local module which enables easy integration of a simple local authentication strategy using usernames and passwords. For the sake of simplicity, in this example (see the next page), we are not using a second backing store, but only an in-memory user instance. In real life applications, the findUser would look up a user in a database. // file:app/index.js const express = require('express') const passport = require('passport') const session = require('express-session') const RedisStore = require('connect-redis')(session) const app = express() app.use(session({ store: new RedisStore({ url: config.redisStore.url }), secret: config.redisStore.secret, resave: false, saveUninitialized: false })) app.use(passport.initialize()) app.use(passport.session()) RisingStack 38 Once the findUser returns with our user object the only thing left is to compare the user-fed and the real password to see if there is a match. If it is a match, we let the user in (by returning the user to passport - return done(null, user)), if not we return an unauthorized error (by returning nothing to passport - return done(null)). Step 3: Adding Protected Endpoints To add protected endpoints, we are leveraging the middleware pattern Express uses. For that, let's create the authentication middleware first: It only has one role if the user is authenticated (has the right cookies) it simply calls the next middleware; otherwise it redirects to the page where the user can log in. // file:app/authenticate/init.js const passport = require('passport') const LocalStrategy = require('passport-local').Strategy const user = { username: 'test-user', password: 'test-password', id: 1 } passport.use(new LocalStrategy( function(username, password, done) { findUser(username, function (err, user) { if (err) { return done(err) } if (!user) { return done(null, false) } if (password !== user.password ) { return done(null, false) } return done(null, user) }) } )) // file:app/user/init.js const passport = require('passport') app.get('/profile', passpo

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