When the user visits root of the website ( / ), a message called “Homepage!” is displayed to the user. But what if he tries to access a URL route which is not defined Ex: /user It displays Cannot GET /users message. We can set up a separate middleware to deal with situations like this. When we encounter a URL which doesn’t have a custom route definition, it’ll look for the file in the public directory, if the file is not found, it’ll look through our final middleware and executes whatever is present inside it.
User Not Found Error Handling In Express: Node.js app.js
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app.use(function(err, req, res, next){
res.send(404, err.message);
next();
});
app.get('/user/:username', function(req, res, next){
if(req.params.username === 'kiran')
{
var err = new Error('User Not Found');
next(err);
}
res.send(req.params.username);
});
app.use(function(err, req, res, next){
res.send(404, err.message);
next();
});
app.get('/user/:username', function(req, res, next){
if(req.params.username === 'kiran')
{
var err = new Error('User Not Found');
next(err);
}
res.send(req.params.username);
});
In real world application, we need to validate the user request before trying to serve them data. Here, if the user requests /user/kiran we’ll let the user know that the user kiran is not present in our database. So we setup a custom error handling middleware for situations like this. Here we create an error object and set a message, and pass this error object as parameter to next. call to next passes the control to the middleware which matches its signature, and executes whatever is present inside the middleware. [ Note the presence of err object inside the middleware callback method. ]
Note: Error handling can significantly increase the performance of your web application, due to the fact that your application need not figure out what to do next, in case of an error. You explicitly write error handling code for most common situations and the application behaves in a predictable manner.
Call to next() passes the execution control to the next level.
We’ve been using middlewares in our previous video tutorials. Today, we’ll have a look at these middlewares.
Connect is a middleware framework of Node.js
But since connect is one of the dependencies of Express, we need not install it separately. If we have installed Express, then we already have connect.
Middeware in Express: Node.js app.js
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var express = require('express');
var app = express();
app.use(express.bodyParser());
app.use(express.methodOverride());
app.use(express.cookieParser());
app.use(express.session({secret: "some secret key"}));
app.use(app.router);
app.use(express.static(path.join(__dirname, 'public')));
var express = require('express');
var app = express(); app.use(express.bodyParser()); app.use(express.methodOverride()); app.use(express.cookieParser()); app.use(express.session({secret: "some secret key"})); app.use(app.router); app.use(express.static(path.join(__dirname, 'public')));
express.bodyParser extensible request body parser express.methodOverride faux HTTP method support express.cookieParser cookie parser express.session session management support with bundled MemoryStore express.static streaming static file server supporting Range and more express.directory directory listing middleware
For list of all supported middleware, visit senchalabs Also check the list of all the 3rd-party middleware supported by Connect.
Note: Ordering of these middleware is very important. For Example: 1. You can only override method after you’ve parsed the body, so methodOverride() must come only after bodyParser() 2. Similarly, session middleware depends on cookieParser(), so session middleware must come only after cookieParser()
As your application becomes popular you’ll need middlewares to handle csrf( Cross-site request forgery ), DDos attacks etc. Also it’s very important to validate the user requests before you allow the user request to fetch the data from your database. Learn to use middleware properly, and I’m sure, it’ll be a life-saver for your application.
When we request information of particular user by using his username in the URL, it fetches the username using request object and displays appropriate message. Example: If the user requests /user/Satish it’ll output Satish’s profile!
Public Folder
If we put some files inside our public directory, it would be convenient if some middlewares fetch the files directly upon user request, instead of writing routes for all those files. Connect module which is a dependency of Express web framework takes care of this.
Middleware for public folder files app.js
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var express = require('express');
var path = require('path');
var app = express();
app.use(express.static(path.join(__dirname, 'public')));
var express = require('express');
var path = require('path');
var app = express(); app.use(express.static(path.join(__dirname, 'public')));
If you want your custom routes to be checked before the public folder, then you could specify it using another middleware, i.e., app.router
Note that, the ordering of Middleware is significant.
Sending HTML in Routs: Express app.js
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app.get('/', function(req, res){
var msg = [
"<h1>I love Google..</h1>",
"<p>Because they make awesome products",
"<br />like my Nexus 7 Tablet",
"which is so amazing!"
].join("\n");
res.send(msg);
});
</p>
app.get('/', function(req, res){ var msg = [ "<h1>I love Google..</h1>", "<p>Because they make awesome products", "<br />like my Nexus 7 Tablet", "which is so amazing!" ].join("\n"); res.send(msg);
});
</p>
This would out put with all HTML semantics on the browser.
Get, Post, Put, Delete Requests Web browsers by default support only get and post requests. But we can override methods and make sure our Node.js application supports even the Put and Delete requests.
Post Request HTML Form index.html present in public directory
Here we have a form with post method and also take note of action field value.
POST Route app.js
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app.use(express.bodyParser());
app.post('/user', function(req, res){
res.send("Submitted user's name is: "+req.body.name);
});
app.use(express.bodyParser());
app.post('/user', function(req, res){ res.send("Submitted user's name is: "+req.body.name);
});
Inorder to parse the HTML page, you’ll need bodyParser middleware. Once you have it in place you can get form field entries and use it to insert the data into database or simply display as in our case with this example.
We could similarly write code for PUT and DELETE requests. PUT & DELETE Routes app.js
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app.use(express.bodyParser());
app.use(express.methodOverride());
app.put('/user/:userId', function(req, res){
res.send("Editing user with userid: "+req.params.userId);
});
app.delete('/user/:userId', function(req, res){
res.send("Editing user with userid: "+req.params.userId);
});
app.use(express.bodyParser());
app.use(express.methodOverride());
app.put('/user/:userId', function(req, res){ res.send("Editing user with userid: "+req.params.userId);
});
app.delete('/user/:userId', function(req, res){ res.send("Editing user with userid: "+req.params.userId);
});
By getting the unique userId of the user, you could fetch the data from database and make changes and update the information using Put request. Similarly, using the unique userId of the user, you could select and delete the information about the user!
Separating Route Files As your application grows, its hard to keep the code cleaner and maintainable, so it’s always a good idea to separate these kind of information from the main application file. So we create a file called routes and include it as a local module in our main application file.
External Route File /routes/index.js
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/*
* GET home page.
*/
exports.index = function(req, res){
res.send('Google Nexus 5 To Be Release Shortly ..');
};
/* * GET home page. */exports.index = function(req, res){ res.send('Google Nexus 5 To Be Release Shortly ..');
};
exports is a global provided by node.js index is a name given by us; it’s a property name and we assign a function to it.
Accessing External Route File app.js
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var routes = require('./routes');
app.get('/', routes.index);
var routes = require('./routes');
app.get('/', routes.index);
This would output: Google Nexus 5 To Be Release Shortly ..
