Express Tutorial Parte 2: Criando a estrutura do website

Nesse artigo mostraremos como criar a estrutura do website usando a ferramenta "Express Application Generator ". Neste caso, usaremos a ferramenta para criar o framework para nosso website "LocalLibrary", para o qual adicionaremos mais tarde todo o outro código necessário para o site. O processo é extremamente simples, com apenas a requisição de invocar o "Generator" na linha de comando com um novo nome de projeto, e, se quiser, especificar o template do site e o gerador de CSS.

As seguintes sessões mostrará como chamar o "Application Generator", e prover uma pequena explicação sobre as diferentes opções de CSS. Também aprenderemos como a estrutura do site é definida. No final, será mostrado como podemos rodar o site para ver se funciona.

Você já deve ter instalado o gerador como requisito. Como um lembrete rápido, você instala a ferramenta de gerador em todo o site usando o Gerenciador de pacotes NPM, como mostrado:

npm install express-generator -g

O gerador tem algumas opções que podem ser visualizadas usando o comando --help (or -h):

> express --help

    Usage: express [options] [dir]


  Options:

        --version        output the version number
    -e, --ejs            add ejs engine support
        --pug            add pug engine support
        --hbs            add handlebars engine support
    -H, --hogan          add hogan.js engine support
    -v, --view <engine>  add view <engine> support (dust|ejs|hbs|hjs|jade|pug|twig|vash) (defaults to jade)
        --no-view        use static html instead of view engine
    -c, --css <engine>   add stylesheet <engine> support (less|stylus|compass|sass) (defaults to plain css)
        --git            add .gitignore
    -f, --force          force on non-empty directory
    -h, --help           output usage information

Você pode simplesmente especificar express para criar um projeto dentro do diretório atual usando Jade view e CSS simples (se você especificar um nome de diretório, o projeto será criado em uma subpasta com esse nome).

express

Também pode ser escolhido um "view" (template) usando--view e/ou um gerador de CSS usando --css.

O Express Application Generator permite que você configure vários mecanismos populares de exibição/modelagem, incluindo EJS, Hbs, Pug (Jade), Twig, e Vash, embora escolha Jade por padrão se você não especificar uma opção de visualização. O próprio Express também pode suportar um grande número de outras linguagens de modelagem out of the box.

De um modo geral, você deve selecionar um mecanismo de modelagem que forneça todas as funcionalidades de que você precisa e permita que você seja mais produtivo - ou em outras palavras, da mesma forma que você escolhe qualquer outro componente! Algumas das coisas a considerar ao comparar mecanismos de modelo:

• Tempo para produtividade — Se sua equipe já tiver experiência com uma linguagem de modelagem, é provável que eles sejam produtivos mais rapidamente usando essa linguagem. Caso contrário, você deve considerar a curva de aprendizado relativa para mecanismos de modelagem candidatos.

• Popularidade e atividade — Revise a popularidade do mecanismo e se ele possui uma comunidade ativa. É importante poder obter suporte para o mecanismo quando você tiver problemas durante a vida útil do site.

• Style — Alguns mecanismos de modelo usam marcação específica para indicar o conteúdo inserido no HTML "comum", enquanto outros constroem o HTML usando uma sintaxe diferente (por exemplo, usando recuo e nomes de bloco).

• Performance/rendering time.

• Features — você deve considerar se os mecanismos que você procura têm os seguintes recursos disponíveis:

  • Layout inheritance: Allows you to define a base template and then "inherit" just the parts of it that you want to be different for a particular page. This is typically a better approach than building templates by including a number of required components or building a template from scratch each time.
  • "Include" support: Allows you to build up templates by including other templates.
  • Concise variable and loop control syntax.
  • Ability to filter variable values at template level (e.g. making variables upper-case, or formatting a date value).
  • Ability to generate output formats other than HTML (e.g. JSON or XML).
  • Support for asynchronous operations and streaming.
  • Can be used on the client as well as the server. If a templating engine can be used on the client this allows the possibility of serving data and having all or most of the rendering done client-side.

Para este projeto, usaremos o Pug mecanismo de modelagem (este é o mecanismo Jade que foi renomeado recentemente), pois esta é uma das linguagens de modelagem Express/JavaScript mais populares e é suportada imediatamente pelo gerador.

The Express Application Generator allows you to create a project that is configured to use the most common CSS stylesheet engines: LESS, SASS, Compass, Stylus.

**Nota:**CSS has some limitations that make certain tasks difficult. CSS stylesheet engines allow you to use more powerful syntax for defining your CSS and then compile the definition into plain-old CSS for browsers to use.

Assim como nos mecanismos de modelagem, você deve usar o mecanismo de folha de estilo que permitirá que sua equipe seja mais produtiva. Para este projeto, usaremos o CSS comum (o padrão), pois nossos requisitos de CSS não são suficientemente complicados para justificar o uso de qualquer outra coisa.

The generated code doesn't use/include any databases. Express apps can use any database mechanism supported by Node (Express itself doesn't define any specific additional behavior/requirements for database management).

We'll discuss how to integrate with a database in a later article.

For the sample Local Library app we're going to build, we'll create a project named express-locallibrary-tutorial using the Pug template library and no CSS stylesheet engine.

Primeiro, navegue até onde deseja criar o projeto e, em seguida, execute o Express Application Generator no prompt de comando, conforme mostrado:

express express-locallibrary-tutorial --view=pug

The generator will create (and list) the project's files.

   create : express-locallibrary-tutorial\
   create : express-locallibrary-tutorial\public\
   create : express-locallibrary-tutorial\public\javascripts\
   create : express-locallibrary-tutorial\public\images\
   create : express-locallibrary-tutorial\public\stylesheets\
   create : express-locallibrary-tutorial\public\stylesheets\style.css
   create : express-locallibrary-tutorial\routes\
   create : express-locallibrary-tutorial\routes\index.js
   create : express-locallibrary-tutorial\routes\users.js
   create : express-locallibrary-tutorial\views\
   create : express-locallibrary-tutorial\views\error.pug
   create : express-locallibrary-tutorial\views\index.pug
   create : express-locallibrary-tutorial\views\layout.pug
   create : express-locallibrary-tutorial\app.js
   create : express-locallibrary-tutorial\package.json
   create : express-locallibrary-tutorial\bin\
   create : express-locallibrary-tutorial\bin\www

   change directory:
     > cd express-locallibrary-tutorial

   install dependencies:
     > npm install

   run the app:
     > SET DEBUG=express-locallibrary-tutorial:* & npm start

At the end of the output, the generator provides instructions on how you install the dependencies (as listed in the package.json file) and then how to run the application (the instructions above are for Windows; on Linux/macOS they will be slightly different).

At this point, we have a complete skeleton project. The website doesn't actually do very much yet, but it's worth running it to show how it works.

1. First, install the dependencies (the install command will fetch all the dependency packages listed in the project's package.json file).

   bash

   cd express-locallibrary-tutorial
   npm install
   

2. Then run the application.

   • On Windows, use this command:

     bash

     SET DEBUG=express-locallibrary-tutorial:* & npm start
     

   • On macOS or Linux, use this command:

     bash

     DEBUG=express-locallibrary-tutorial:* npm start
     

3. Then load http://localhost:3000/ in your browser to access the app.

You should see a browser page that looks like this:

You have a working Express application, serving itself to localhost:3000.

>SET DEBUG=express-locallibrary-tutorial:* & npm start

> express-locallibrary-tutorial@0.0.0 start D:\github\mdn\test\exprgen\express-locallibrary-tutorial
> node ./bin/www

  express-locallibrary-tutorial:server Listening on port 3000 +0ms
GET / 304 490.296 ms - -
GET /stylesheets/style.css 200 4.886 ms - 111

Any changes you make to your Express website are currently not visible until you restart the server. It quickly becomes very irritating to have to stop and restart your server every time you make a change, so it is worth taking the time to automate restarting the server when needed.

One of the easiest such tools for this purpose is nodemon. This is usually installed globally (as it is a "tool"), but here we'll install and use it locally as a developer dependency, so that any developers working with the project get it automatically when they install the application. Use the following command in the root directory for the skeleton project:

npm install --save-dev nodemon

If you still choose to install nodemon globally to your machine, and not only to your project's package.json file:

npm install -g nodemon

If you open your project's package.json file you'll now see a new section with this dependency:

 "devDependencies": {
    "nodemon": "^1.18.10"
}

Because the tool isn't installed globally we can't launch it from the command line (unless we add it to the path) but we can call it from an NPM script because NPM knows all about the installed packages. Find the the scripts section of your package.json. Initially, it will contain one line, which begins with "start". Update it by putting a comma at the end of that line, and adding the "devstart" line seen below:

  "scripts": {
    "start": "node ./bin/www",
    "devstart": "nodemon ./bin/www"
  },

We can now start the server in almost exactly the same way as previously, but with the devstart command specified:

• On Windows, use this command:

  bash

  SET DEBUG=express-locallibrary-tutorial:* & npm run devstart
  

• On macOS or Linux, use this command:

  bash

  DEBUG=express-locallibrary-tutorial:* npm run devstart
  

Let's now take a look at the project we just created.

The generated project, now that you have installed dependencies, has the following file structure (files are the items not prefixed with "/"). The package.json file defines the application dependencies and other information. It also defines a startup script that will call the application entry point, the JavaScript file /bin/www. This sets up some of the application error handling and then loads app.js to do the rest of the work. The app routes are stored in separate modules under the routes/ directory. The templates are stored under the /views directory.

/express-locallibrary-tutorial
    app.js
    /bin
        www
    package.json
    package-lock.json
    /node_modules
        [about 6700 subdirectories and files]
    /public
        /images
        /javascripts
        /stylesheets
            style.css
    /routes
        index.js
        users.js
    /views
        error.pug
        index.pug
        layout.pug

The following sections describe the files in a little more detail.

The package.json file defines the application dependencies and other information:

{
  "name": "express-locallibrary-tutorial",
  "version": "0.0.0",
  "private": true,
  "scripts": {
    "start": "node ./bin/www",
    "devstart": "nodemon ./bin/www"
  },
  "dependencies": {
    "cookie-parser": "~1.4.3",
    "debug": "~2.6.9",
    "express": "~4.16.0",
    "http-errors": "~1.6.2",
    "morgan": "~1.9.0",
    "pug": "2.0.0-beta11"
  },
  "devDependencies": {
    "nodemon": "^1.18.10"
  }
}

The dependencies include the express package and the package for our selected view engine (pug). In addition, we have the following packages that are useful in many web applications:

• cookie-parser: Used to parse the cookie header and populate req.cookies (essentially provides a convenient method for accessing cookie information).
• debug: A tiny node debugging utility modeled after node core's debugging technique.
• morgan: An HTTP request logger middleware for node.
• http-errors: Create HTTP errors where needed (for express error handling).

The scripts section defines a "start" script, which is what we are invoking when we call npm start to start the server. From the script definition, you can see that this actually starts the JavaScript file ./bin/www with node. It also defines a "devstart" script, which we invoke when calling npm run devstart instead. This starts the same ./bin/www file, but with nodemon rather than node.

  "scripts": {
    "start": "node ./bin/www",
    "devstart": "nodemon ./bin/www"
  },

The file /bin/www is the application entry point! The very first thing this does is require() the "real" application entry point (app.js, in the project root) that sets up and returns the express() application object.

#!/usr/bin/env node

/**
 * Module dependencies.
 */

var app = require("../app");

The remainder of the code in this file sets up a node HTTP server with app set to a specific port (defined in an environment variable or 3000 if the variable isn't defined), and starts listening and reporting server errors and connections. For now you don't really need to know anything else about the code (everything in this file is "boilerplate"), but feel free to review it if you're interested.

This file creates an express application object (named app, by convention), sets up the application with various settings and middleware, and then exports the app from the module. The code below shows just the parts of the file that create and export the app object:

var express = require('express');
var app = express();
...
module.exports = app;

Back in the www entry point file above, it is this module.exports object that is supplied to the caller when this file is imported.

Let's work through the app.js file in detail. First, we import some useful node libraries into the file using require(), including http-errors, express, morgan and cookie-parser that we previously downloaded for our application using NPM; and path, which is a core Node library for parsing file and directory paths.

var createError = require("http-errors");
var express = require("express");
var path = require("path");
var cookieParser = require("cookie-parser");
var logger = require("morgan");

Then we require() modules from our routes directory. These modules/files contain code for handling particular sets of related "routes" (URL paths). When we extend the skeleton application, for example to list all books in the library, we will add a new file for dealing with book-related routes.

var indexRouter = require("./routes/index");
var usersRouter = require("./routes/users");

Next, we create the app object using our imported express module, and then use it to set up the view (template) engine. There are two parts to setting up the engine. First, we set the 'views' value to specify the folder where the templates will be stored (in this case the subfolder /views). Then we set the 'view engine' value to specify the template library (in this case "pug").

var app = express();

// view engine setup
app.set("views", path.join(__dirname, "views"));
app.set("view engine", "pug");

The next set of functions call app.use() to add the middleware libraries into the request handling chain. In addition to the 3rd party libraries we imported previously, we use the express.static middleware to get Express to serve all the static files in the /public directory in the project root.

app.use(logger("dev"));
app.use(express.json());
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, "public")));

Now that all the other middleware is set up, we add our (previously imported) route-handling code to the request handling chain. The imported code will define particular routes for the different parts of the site:

app.use("/", indexRouter);
app.use("/users", usersRouter);

The last middleware in the file adds handler methods for errors and HTTP 404 responses.

// catch 404 and forward to error handler
app.use(function (req, res, next) {
  next(createError(404));
});

// error handler
app.use(function (err, req, res, next) {
  // set locals, only providing error in development
  res.locals.message = err.message;
  res.locals.error = req.app.get("env") === "development" ? err : {};

  // render the error page
  res.status(err.status || 500);
  res.render("error");
});

The Express application object (app) is now fully configured. The last step is to add it to the module exports (this is what allows it to be imported by /bin/www).

module.exports = app;

The route file /routes/users.js is shown below (route files share a similar structure, so we don't need to also show index.js). First, it loads the express module and uses it to get an express.Router object. Then it specifies a route on that object and lastly exports the router from the module (this is what allows the file to be imported into app.js).

var express = require("express");
var router = express.Router();

/* GET users listing. */
router.get("/", function (req, res, next) {
  res.send("respond with a resource");
});

module.exports = router;

The route defines a callback that will be invoked whenever an HTTP GET request with the correct pattern is detected. The matching pattern is the route specified when the module is imported ('/users') plus whatever is defined in this file ('/'). In other words, this route will be used when an URL of /users/ is received.

One thing of interest above is that the callback function has the third argument 'next', and is hence a middleware function rather than a simple route callback. While the code doesn't currently use the next argument, it may be useful in the future if you want to add multiple route handlers to the '/' route path.

The views (templates) are stored in the /views directory (as specified in app.js) and are given the file extension .pug. The method Response.render() is used to render a specified template along with the values of named variables passed in an object, and then send the result as a response. In the code below from /routes/index.js you can see how that route renders a response using the template "index" passing the template variable "title".

/* GET home page. */
router.get("/", function (req, res, next) {
  res.render("index", { title: "Express" });
});

The corresponding template for the above route is given below (index.pug). We'll talk more about the syntax later. All you need to know for now is that the title variable (with value 'Express') is inserted where specified in the template.

extends layout

block content
  h1= title
  p Welcome to #{title}

Create a new route in /routes/users.js that will display the text "You're so cool" at URL /users/cool/. Test it by running the server and visiting http://localhost:3000/users/cool/ in your browser

You have now created a skeleton website project for the Local Library and verified that it runs using node. Most importantly, you also understand how the project is structured, so you have a good idea where we need to make changes to add routes and views for our local library.

Next, we'll start modifying the skeleton so that it works as a library website.

• Express application generator (Express docs)
• Using template engines with Express (Express docs)

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