const app = express()
Add a new route method to handle requests for the path "/". The first argument specifies the path or URL, the next argument is the route handler. Inside the route handler, let's use the response object to send a status code 200 (OK) and text to the client
Finally, use the listen method to accept new connections on port 1337:
app.listen(1337, () => console.log('Web Server running on port 1337'),)
Initial
create new
var express = require('express');
var app = express();
app.get('/', function(req, res){
res.send('hello world');
});
app.listen(3000);
Router :
We can use app.route()
app.route('/book')
.get(function(req, res) {
res.send('Get a random book');
})
.post(function(req, res) {
res.send('Add a book');
})
.put(function(req, res) {
res.send('Update the book');
});
Routing refers to determining how an application responds to a client request to a particular endpoint, which is a URI (or path) and a specific HTTP request method (GET, POST, and so on).
app.METHOD(PATH, HANDLER);
A router object is an isolated instance of middleware and routes. You can think of it as a “mini-application,” capable only of performing middleware and routing functions. Every Express application has a built-in app router
CRUD
// GET method route
app.get('/', function (req, res) {
res.send('GET request to the homepage');
});
// POST method route
app.post('/', function (req, res) {
res.send('POST request to the homepage');
});
app.put('/user', function(req, res) {
res.send('Got a PUT request at /user');
});
app.delete('/user', function(req, res) {
res.send('Got a DELETE request at /user');
});
Respond to all METHOD to the /user route:
app.all('/user', function(req, res) {
res.send('Got a request at /user');
});
const express = require('express');
const router = express.Router();
// middleware that is specific to this router
router.use(function timeLog(req, res, next) {
console.log('request for books - Time: ', Date.now());
next();
});
// define the home page route
router.get('/', function(req, res) {
res.send('Books home page');
});
// define the about route
router.get('/about', function(req, res) {
res.send('About books');
});
module.exports = router;
Advanced Routing
regular expression
[abc] Matches either an a, b or c character
[a-z] Matches any characters between a and z, including a and z.
. Matches any character other than newline
\d Matches any decimal digit. Equivalent to [0-9].
In Express, 404 responses are not the result of an error, so the error-handler middleware will not capture them. This behavior is because a 404 response simply indicates the absence of additional work to do; in other words, Express has executed all middleware functions and routes, and found that none of them responded. All you need to do is add a middleware function at the very bottom of the stack (below all other functions) to handle a 404 response:
app.use(function(req, res, next) {
res.status(404).send("Sorry can't find that!");
});
app.use(function(err, req, res, next) {
console.error(err.stack);
res.status(500).send('Something broke!');
});
app.get('/error', function (req, res) {
throw new Error('BROKEN') // Express will catch this on its own.
})
app.get('/', function (req, res, next) {
fs.readFile('/file-does-not-exist', function (err, data) {
if (err) {
next(err) // Pass errors to Express.
} else {
res.send(data)
}
})
})
Express Middleware
app.use app.METHOD()
router.use router.METHOD()
err app.use(function(err, req,res,next))
import, third party middleware
router.use('url',function(req,res,next){next()})
app.use('url', function(req,res,next){next()})
Middleware functions are functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle. The next middleware function is commonly denoted by a variable named next.
Middleware functions can perform the following tasks:
Execute any code.
Make changes to the request and the response objects.
// define the home page route
router.get('/', function(req, res) {
res.send('Books home page');
});
Example - Error Handling
You define error-handling middleware in the same way as other middleware, except with four arguments instead of three; specifically with the signature (err, req, res, next):
