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This second article in our Express Tutorial shows how you can create a "skeleton" website project which you can then go on to populate with site-specific routes, templates/views, and database calls.
| Prerequisites: | Set up a Node development environment. Review the Express Tutorial. |
|---|---|
| Objective: | Express 앱 제너레이터를 사용하여 자신만의 새로운 웹사이트 프로젝트를 시작할 수 있다. |
이 아티클은 당신이 Express Application Generator 도구를 이용하여 스켈레톤(최소한의 프레임 모형만 갖춘) 웹사이트를 만드는 방법을 보여줍니다. 이는 사이트에 맞춘 라우트, 뷰/템플릿 그리고 데이터 베이스를 사용할 수 있게 합니다. In this case, we'll use the tool to create the framework for our Local Library website, to which we'll later add all the other code needed by the site. The process is extremely simple, requiring only that you invoke the generator on the command line with a new project name, optionally also specifying the site's template engine and CSS generator.
The following sections show you how to call the application generator, and provides a little explanation about the different view/CSS options. We'll also explain how the skeleton website is structured. At the end, we'll show how you can run the website to verify that it works.
Note: The Express Application Generator is not the only generator for Express applications, and the generated project is not the only viable way to structure your files and directories. The generated site does however have a modular structure that is easy to extend and understand. For information about a minimal Express application, see Hello world example (Express docs).
You should already have installed the generator as part of setting up a Node development environment. As a quick reminder, you install the generator tool site-wide using the NPM package manager, as shown:
npm install express-generator -gThe generator has a number of options, which you can view on the command line using the --help (or -h) command:
> 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
You can simply specify express to create a project inside the current directory using the Jade view engine and plain CSS (if you specify a directory name then the project will be created in a sub-folder with that name).
expressYou can also choose a view (template) engine using --view and/or a CSS generation engine using --css.
Note: The other options for choosing template engines (e.g. --hogan, --ejs, --hbs etc.) are deprecated. Use --view (or -v)!
The Express Application Generator allows you to configure a number of popular view/templating engines, including EJS, Hbs, Pug (Jade), Twig, and Vash, although it chooses Jade by default if you don't specify a view option. Express itself can also support a large number of other templating languages out of the box.
Note: If you want to use a template engine that isn't supported by the generator then see Using template engines with Express (Express docs) and the documentation for your target view engine.
Generally speaking, you should select a templating engine that delivers all the functionality you need and allows you to be productive sooner — or in other words, in the same way that you choose any other component! Some of the things to consider when comparing template engines:
Tip: There are many resources on the Internet to help you compare the different options!
For this project, we'll use the Pug templating engine (this is the recently-renamed Jade engine), as this is one of the most popular Express/JavaScript templating languages and is supported out of the box by the generator.
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.
Note: 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.
As with templating engines, you should use the stylesheet engine that will allow your team to be most productive. For this project, we'll use the ordinary CSS (the default) as our CSS requirements are not sufficiently complicated to justify using anything else.
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.
Local Library 샘플 앱을 위해서 우리는 express-locallibrary-tutorial 라는 이름의 프로젝트를 생성할 것입니다. Pug 라는(jade의 후속격) 템플릿 라이브러리를 사용할 것이며, CSS stylesheet 엔진은 사용하지 않습니다.
First, navigate to where you want to create the project and then run the Express Application Generator in the command prompt as shown:
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).
Note: When using Windows, the && and & assumes you are using the Command Prompt. If you are using the new default PowerShell terminal do not concatenate the commands with && and &. Instead set the DEBUG environment variable with $ENV:DEBUG = "express-locallibrary-tutorial:*";. The npm start can be followed by the npm start.
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.
install command will fetch all the dependency packages listed in the project's package.json file).
cd express-locallibrary-tutorial npm install
SET DEBUG=express-locallibrary-tutorial:* & npm start
DEBUG=express-locallibrary-tutorial:* npm start
You should see a browser page that looks like this:
You have a working Express application, serving itself to localhost:3000.
Note: You could also start the app just using the npm start command. Specifying the DEBUG variable as shown enables console logging/debugging. For example, when you visit the above page you'll see debug output like this:
>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",
"serverstart": "DEBUG=express-locallibrary-tutorial:* npm run devstart"
},
We can now start the server in almost exactly the same way as previously, but with the devstart command specified:
SET DEBUG=express-locallibrary-tutorial:* & npm run devstart
DEBUG=express-locallibrary-tutorial:* npm run devstart
Note: Now if you edit any file in the project the server will restart (or you can restart it by typing rs on the command prompt at any time). You will still need to reload the browser to refresh the page.
We now have to call "npm run <scriptname>" rather than just npm start, because "start" is actually an NPM command that is mapped to the named script. We could have replaced the command in the start script but we only want to use nodemon during development, so it makes sense to create a new script command.
The serverstart command added to the scripts in the package.json above is a very good example. Using this approach means you no longer have to type a long command shown to start the server. Note that the particular command added to the script works for macOS or Linux only.
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:
req.cookies (essentially provides a convenient method for accessing cookie information).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');
Note: require() is a global node function that is used to import modules into the current file. Here we specify app.js module using a relative path and omitting the optional (.js) file extension.
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');
Note: At this point, we have just imported the module; we haven't actually used its routes yet (this happens just a little bit further down the file).
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);
Note: The paths specified above ('/' and '/users') are treated as a prefix to routes defined in the imported files. So for example, if the imported users module defines a route for /profile, you would access that route at /users/profile. We'll talk more about routes in a later article.
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.
Tip: Try this out by running the server with node and visiting the URL in your browser: http://localhost:3000/users/. You should see a message: 'respond with a resource'.
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.
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