Express.js ialah rangka kerja aplikasi web Node.js yang minimum dan fleksibel yang menyediakan set ciri yang mantap untuk aplikasi web dan mudah alih. Ia memudahkan membina aplikasi dan API sebelah pelayan, mengendalikan permintaan HTTP dan mengurus perisian tengah.
Langkah untuk Memasang dan Menyediakan Express.js:
Pasang Node.js:
Buat Direktori Projek Baharu:
mkdir my-express-app cd my-express-app
npm init -y
Arahan ini mencipta fail package.json dengan tetapan lalai.
npm install express
Arahan ini memasang Express.js dan menambahkannya sebagai kebergantungan dalam fail package.json anda.
npm install --save-dev nodemon
"scripts": {
"start": "nodemon app.js"
}
Sediakan Sintaks Import untuk JavaScript:
"type": "module"
Buat Fail Titik Kemasukan:
Buat fail bernama app.js (atau index.js) dalam direktori projek anda. Fail ini akan mengandungi kod aplikasi Express anda.
Untuk mencipta aplikasi Ekspres asas, ikut langkah berikut:
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}`);
});
Jalankan Aplikasi:
npm start
Dengan langkah ini, anda telah menyediakan aplikasi Express.js asas menggunakan sintaks import ES6 dan nodemon yang dikonfigurasikan untuk memulakan semula pelayan secara automatik semasa pembangunan. Persediaan ini membantu memperkemas pembangunan dan mengendalikan perubahan kod dengan cekap.
Penghalaan dalam Express.js ialah proses menentukan cara aplikasi bertindak balas kepada permintaan pelanggan untuk titik akhir tertentu. Laluan boleh ditakrifkan untuk kaedah HTTP yang berbeza (GET, POST, PUT, DELETE, dll.) dan boleh diatur untuk mengendalikan struktur URL yang kompleks.
Laluan GET digunakan untuk mendapatkan semula data daripada pelayan. Ia sering digunakan untuk menyampaikan kandungan statik atau data berdasarkan pertanyaan.
Contoh:
// Basic GET route
app.get('/home', (req, res) => {
res.send('Welcome to the Home Page!');
});
Laluan POST digunakan untuk menghantar data ke pelayan. Ia biasanya digunakan untuk menyerahkan borang atau mencipta sumber baharu.
Contoh:
// Basic POST route
app.post('/submit', (req, res) => {
res.send('Form submitted!');
});
Laluan PUT digunakan untuk mengemas kini data sedia ada pada pelayan. Ia biasanya digunakan untuk mengubah suai sumber atau mengemas kini rekod.
Contoh:
// Basic PUT route
app.put('/update', (req, res) => {
res.send('Data updated!');
});
Laluan DELETE digunakan untuk mengalih keluar data daripada pelayan. Ia digunakan untuk memadam sumber atau rekod.
Contoh:
// Basic DELETE route
app.delete('/delete', (req, res) => {
res.send('Data deleted!');
});
Kaedah app.use dalam Express.js digunakan untuk mendaftarkan fungsi middleware yang mengendalikan permintaan. Fungsi middleware dilaksanakan mengikut susunan yang ditakrifkan dan app.use boleh digunakan untuk menggunakan middleware secara global atau pada laluan tertentu.
Apabila app.use digunakan tanpa laluan, fungsi middleware digunakan pada semua permintaan masuk. Ini berguna untuk menyediakan kefungsian global seperti pengelogan, menghuraikan badan permintaan atau sesi pengendalian.
Contoh:
// 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
});
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