Express.js ist ein minimales und flexibles Node.js-Webanwendungs-Framework, das einen robusten Satz an Funktionen für Web- und mobile Anwendungen bietet. Es vereinfacht die Erstellung serverseitiger Anwendungen und APIs, die Verarbeitung von HTTP-Anfragen und die Verwaltung von Middleware.
Schritte zum Installieren und Einrichten von Express.js:
Node.js installieren:
Neues Projektverzeichnis erstellen:
mkdir my-express-app cd my-express-app
npm init -y
Dieser Befehl erstellt eine package.json-Datei mit Standardeinstellungen.
npm install express
Dieser Befehl installiert Express.js und fügt es als Abhängigkeit in Ihrer package.json-Datei hinzu.
npm install --save-dev nodemon
"scripts": {
"start": "nodemon app.js"
}
Importsyntax für JavaScript einrichten:
"type": "module"
Erstellen Sie die Einstiegspunktdatei:
Erstellen Sie eine Datei mit dem Namen app.js (oder index.js) in Ihrem Projektverzeichnis. Diese Datei enthält Ihren Express-Anwendungscode.
Um eine einfache Express-Anwendung zu erstellen, befolgen Sie diese Schritte:
import express from 'express';
const app = express();
const port = 3000;
app.get('/', (req, res) => {
res.send('Hello, World!');
});
app.listen(port, () => {
console.log(`Server is running on http://localhost:${port}`);
});
Führen Sie die Anwendung aus:
npm start
Mit diesen Schritten haben Sie eine grundlegende Express.js-Anwendung mit der ES6-Importsyntax eingerichtet und Nodemon so konfiguriert, dass der Server während der Entwicklung automatisch neu gestartet wird. Dieses Setup trägt dazu bei, die Entwicklung zu rationalisieren und Codeänderungen effizient zu handhaben.
Routing in Express.js ist der Prozess der Definition, wie eine Anwendung auf Clientanfragen für bestimmte Endpunkte reagiert. Routen können für verschiedene HTTP-Methoden (GET, POST, PUT, DELETE usw.) definiert und so organisiert werden, dass sie komplexe URL-Strukturen verarbeiten.
Eine GET-Route wird verwendet, um Daten vom Server abzurufen. Es wird häufig verwendet, um statische Inhalte oder Daten basierend auf einer Abfrage bereitzustellen.
Beispiel:
// Basic GET route
app.get('/home', (req, res) => {
res.send('Welcome to the Home Page!');
});
Eine POST-Route wird verwendet, um Daten an den Server zu senden. Es wird häufig zum Senden von Formularen oder zum Erstellen neuer Ressourcen verwendet.
Beispiel:
// Basic POST route
app.post('/submit', (req, res) => {
res.send('Form submitted!');
});
Eine PUT-Route wird verwendet, um vorhandene Daten auf dem Server zu aktualisieren. Es wird normalerweise verwendet, um Ressourcen zu ändern oder Datensätze zu aktualisieren.
Beispiel:
// Basic PUT route
app.put('/update', (req, res) => {
res.send('Data updated!');
});
Eine DELETE-Route wird verwendet, um Daten vom Server zu entfernen. Es wird zum Löschen von Ressourcen oder Datensätzen verwendet.
Beispiel:
// Basic DELETE route
app.delete('/delete', (req, res) => {
res.send('Data deleted!');
});
Die app.use-Methode in Express.js wird verwendet, um Middleware-Funktionen zu registrieren, die Anfragen verarbeiten. Middleware-Funktionen werden in der Reihenfolge ausgeführt, in der sie definiert sind, und app.use kann verwendet werden, um Middleware global oder auf bestimmte Pfade anzuwenden.
Wenn app.use ohne Pfad verwendet wird, wird die Middleware-Funktion auf alle eingehenden Anfragen angewendet. Dies ist nützlich zum Einrichten globaler Funktionen wie Protokollierung, Parsen von Anforderungstexten oder Bearbeiten von Sitzungen.
Beispiel:
// Middleware function applied globally
app.use((req, res, next) => {
console.log(`Request URL: ${req.url}`);
next(); // Pass control to the next handler
});
app.get('/', (req, res) => {
res.send('Home Page');
});
You can use app.use to apply middleware only to requests that match a specific path. This allows you to target middleware to certain routes.
Example:
// Middleware function applied to /admin paths
app.use('/admin', (req, res, next) => {
console.log('Admin route accessed');
next(); // Pass control to the next handler
});
app.get('/admin/dashboard', (req, res) => {
res.send('Admin Dashboard');
});
app.get('/user/profile', (req, res) => {
res.send('User Profile');
});
You can chain multiple middleware functions together with app.use, allowing for sequential processing of requests.
Example:
// First middleware function
const firstMiddleware = (req, res, next) => {
console.log('First Middleware');
next(); // Proceed to the next middleware
};
// Second middleware function
const secondMiddleware = (req, res, next) => {
console.log('Second Middleware');
next(); // Proceed to the next handler
};
// Apply multiple middleware functions
app.use(firstMiddleware, secondMiddleware);
app.get('/', (req, res) => {
res.send('Home Page');
});
The app.use method in Express.js provides flexibility for applying middleware functions globally or to specific routes, and for processing requests in a modular fashion.
In Express.js, callback functions are crucial for handling HTTP requests. They are used in middleware and route handlers to process requests and manage responses.
Callback functions in Express.js receive three parameters:
Example:
function callback(req, res, next) {
// Your code here
next(); // Pass control to the next middleware or route handler
}
Middleware functions process requests before they reach route handlers. They utilize the req, res, and next parameters.
Example:
const logMiddleware = (req, res, next) => {
console.log(`Request URL: ${req.url}`);
next(); // Pass control to the next handler
};
app.use(logMiddleware); // Apply middleware globally
app.get('/', (req, res) => {
res.send('Home Page');
});
Route handlers define responses for specific routes, using callback parameters to manage requests and responses.
Example:
app.get('/example', (req, res) => {
res.send('Hello World!');
});
Multiple middleware functions can be chained together to handle requests sequentially.
Example:
const authenticate = (req, res, next) => {
console.log('Authentication middleware');
next(); // Proceed to the next middleware
};
const authorize = (req, res, next) => {
console.log('Authorization middleware');
next(); // Proceed to the route handler
};
app.get('/profile', authenticate, authorize, (req, res) => {
res.send('User Profile');
});
Route parameters are dynamic segments of a URL used to capture values from the URL path. They allow you to define routes that can handle variable input, making your routes more flexible.
Route parameters are defined in the route path by using a colon : followed by the parameter name. You can access these parameters in your route handler through the req.params object.
Example:
// Route with a route parameter
app.get('/user/:id', (req, res) => {
const userId = req.params.id;
res.send(`User ID: ${userId}`);
});
You can define multiple route parameters in a single route path, allowing for more complex URL structures.
Example:
// Route with multiple route parameters
app.get('/post/:year/:month/:day', (req, res) => {
const { year, month, day } = req.params;
res.send(`Post date: ${year}-${month}-${day}`);
});
Route parameters can also be optional. Use a question mark ? to indicate optional segments in the route path.
Example:
// Route with an optional route parameter
app.get('/product/:id?', (req, res) => {
const productId = req.params.id || 'not specified';
res.send(`Product ID: ${productId}`);
});
Route parameters provide a way to build dynamic and flexible routes in Express.js, allowing you to handle various input values and create more sophisticated URL patterns.
In Express.js, the req object represents the incoming HTTP request from the client. It includes details about the request such as URL, headers, and body. Properly understanding the req object is crucial for handling requests effectively.
The req.body property contains data sent in the request body, typically used in POST and PUT requests. To access req.body, you need to use middleware for parsing the request data.
Handling JSON Data:
app.use(express.json()); // Middleware to parse JSON bodies
app.post('/submit', (req, res) => {
const { name, age } = req.body;
res.send(`Received data - Name: ${name}, Age: ${age}`);
});
Handling URL-encoded Data:
app.use(express.urlencoded({ extended: true })); // Middleware to parse URL-encoded bodies
app.post('/submit', (req, res) => {
const { name, age } = req.body;
res.send(`Received data - Name: ${name}, Age: ${age}`);
});
The req.cookies property contains cookies sent by the client. To use req.cookies, you need the cookie-parser middleware to parse cookies in requests.
Example:
import cookieParser from 'cookie-parser';
app.use(cookieParser()); // Middleware to parse cookies
app.get('/check-cookies', (req, res) => {
const user = req.cookies.user; // Access a cookie named 'user'
res.send(`Cookie value - User: ${user}`);
});
The req.method property contains the HTTP method of the incoming request. This can be useful for handling different types of requests, such as GET, POST, PUT, DELETE, etc.
Example:
app.use((req, res, next) => {
console.log(`Request Method: ${req.method}`); // Logs the HTTP method of the request
next(); // Pass control to the next handler
});
app.get('/example', (req, res) => {
res.send(`This is a GET request`);
});
app.post('/example', (req, res) => {
res.send(`This is a POST request`);
});
The req.params property contains route parameters specified in the URL path. Route parameters are used to capture values from the URL and are typically defined in routes with a colon syntax (e.g., /users/:id).
Example:
app.get('/users/:id', (req, res) => {
const userId = req.params.id; // Access the route parameter 'id'
res.send(`User ID: ${userId}`);
});
The req.query property contains query string parameters from the URL. These are typically used to pass data in the URL for GET requests.
Example:
app.get('/search', (req, res) => {
const query = req.query.q; // Access the query parameter 'q'
res.send(`Search query: ${query}`);
});
The req.get() method is used to retrieve HTTP headers from the incoming request. It allows you to access specific headers by name. This is useful for extracting metadata about the request or for handling custom headers.
Example:
app.get('/headers', (req, res) => {
const userAgent = req.get('User-Agent'); // Access the 'User-Agent' header
const host = req.get('Host'); // Access the 'Host' header
const acceptLanguage = req.get('Accept-Language'); // Access the 'Accept-Language' header
const contentType = req.get('Content-Type'); // Access the 'Content-Type' header
res.send(`
User-Agent: ${userAgent}<br>
Host: ${host}<br>
Accept-Language: ${acceptLanguage}<br>
Content-Type: ${contentType}
`);
});
In Express.js, the res object represents the HTTP response that is sent back to the client. It is used to set response headers, status codes, and to send data or files back to the client. Understanding the res object is essential for controlling the response sent from the server.
The res.append() method is used to add additional headers to the response. It is useful when you need to modify or add headers dynamically before sending the response.
Example:
app.get('/set-headers', (req, res) => {
res.append('Custom-Header', 'HeaderValue'); // Add a custom header
res.append('Another-Header', 'AnotherValue'); // Add another header
res.send('Headers have been set!');
});
The res.cookie() method is used to set cookies on the client's browser. It allows you to send cookies with specific options such as expiration, path, and secure flags.
Example:
app.get('/set-cookie', (req, res) => {
// Set a cookie named 'username' with a value 'JohnDoe'
res.cookie('username', 'JohnDoe', {
maxAge: 24 * 60 * 60 * 1000, // Cookie expires after 1 day
httpOnly: true, // Cookie is not accessible via JavaScript
secure: false, // Cookie is sent over HTTP (not HTTPS)
path: '/' // Cookie is valid for the entire domain
});
res.send('Cookie has been set');
});
The res.end() method is used to end the response process and send the response to the client. It is often used to send the final output or to close the response stream when no additional data needs to be sent.
Example:
app.get('/finish', (req, res) => {
res.end('Response has been sent and the connection is closed.');
});
The res.json() method is used to send a JSON response to the client. It automatically sets the Content-Type header to application/json and converts the provided data into a JSON string.
Example:
app.get('/data', (req, res) => {
const data = {
name: 'John Doe',
age: 30,
city: 'New York'
};
res.json(data);
});
The res.location() method sets the Location header of the response. It is commonly used to specify the URL to which a client should be redirected. However, this method does not send a response to the client by itself; it only sets the header.
Example:
app.get('/set-location', (req, res) => {
res.location('/new-url');
res.send('Location header has been set');
});
The res.redirect() method sends a redirect response to the client. It sets the Location header and sends a status code (default is 302) to redirect the client to a different URL.
Example:
app.get('/redirect', (req, res) => {
res.redirect('/new-url');
});
The res.send() method is used to send a response to the client. It can send a variety of response types, including strings, buffers, objects, or arrays. The method automatically sets the Content-Type header based on the type of the response.
Example:
app.get('/text', (req, res) => {
res.send('This is a plain text response.');
});
app.get('/json', (req, res) => {
const data = { message: 'This is a JSON response.' };
res.send(data);
});
app.get('/buffer', (req, res) => {
const buffer = Buffer.from('This is a buffer response.');
res.send(buffer);
});
The res.sendFile() method is used to send a file as the response to the client. It sets the appropriate Content-Type header based on the file type and streams the file to the client.
Example:
import path from 'path';
app.get('/file', (req, res) => {
const filePath = path.join(__dirname, 'public', 'example.txt');
res.sendFile(filePath);
});
The res.sendStatus() method sets the HTTP status code and sends the corresponding status message as the response body. It is a shorthand for setting the status code and sending a response in one step.
Example:
app.get('/status', (req, res) => {
res.sendStatus(404); // Sends a 404 Not Found status with the message 'Not Found'
});
The res.set() method sets HTTP headers for the response. It can be used to specify various headers, including custom headers.
Example:
app.get('/headers', (req, res) => {
res.set('X-Custom-Header', 'Value');
res.set({
'Content-Type': 'application/json',
'X-Another-Header': 'AnotherValue'
});
res.send('Headers set');
});
The res.status() method sets the HTTP status code for the response. This method is used to define the status code before sending the response.
Example:
app.get('/error', (req, res) => {
res.status(500).send('Internal Server Error'); // Sets status code to 500 and sends the message
});
Das obige ist der detaillierte Inhalt vonVollständiger Express.js-Leitfaden. Für weitere Informationen folgen Sie bitte anderen verwandten Artikeln auf der PHP chinesischen Website!
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