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Express JavaScript

Guide to the Express Response Object — Redirection and Templates

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The Express response object lets us send a response to the client.

Various kinds of responses like strings, JSON, and files can be sent. Also, we can send various headers and status code to the client in addition to the body.

In this article, we’ll look at various properties of the response object, including sending the Links response header, redirect to different paths and URLs, and rendering HTML.

Methods

res.links(links)

The links method joins an object with links together and sends the Link response header with the links joined together.

For example, we can use it as follows:

const express = require('express');  
const bodyParser = require('body-parser');
const app = express();app.use(bodyParser.json());  
app.use(bodyParser.urlencoded({ extended: true }));
app.get('/', (req, res) => {  
  res  
    .links({  
      next: 'http://foo.com?page=1',  
      last: 'http://foo.com?page=2'
    })  
    .send();  
});
app.listen(3000, () => console.log('server started'));

Then we get that the Link response header has the value:

<http://foo.com?page=1>; rel="next", <http://foo.com?page=2>; rel="last"

when we make a request to the / path.

res.location(path)

The location method sends the Location response header with the specified path parameter as the value.

For example, we can use it as follows:

const express = require('express');  
const bodyParser = require('body-parser');
const app = express();app.use(bodyParser.json());  
app.use(bodyParser.urlencoded({ extended: true }));
app.get('/', (req, res) => {  
  res  
    .location('http://medium.com')  
    .send();  
});
app.listen(3000, () => console.log('server started'));

Then we get:

http://medium.com

as the value of the Location response header when we make a request to the / route.

res.redirect([status,] path)

The redirect method redirects to the URL or path specified with the specified status . If no status is specified, the default is 302.

For example, we can use it as follows to redirect to another route:

const express = require('express');  
const bodyParser = require('body-parser');
const app = express();app.use(bodyParser.json());  
app.use(bodyParser.urlencoded({ extended: true }));
app.get('/', (req, res) => {  
  res.redirect('/bar');  
});

app.get('/bar', (req, res) => {  
  res.send('bar');  
});

app.listen(3000, () => console.log('server started'));

Then we should see bar since we redirected to the bar route.

We can specify a status code as follows:

const express = require('express');  
const bodyParser = require('body-parser');
const app = express();app.use(bodyParser.json());  
app.use(bodyParser.urlencoded({ extended: true }));
app.get('/', (req, res) => {  
  res.redirect(301, '/bar');  
});

app.get('/bar', (req, res) => {  
  res.send('bar');  
});

app.listen(3000, () => console.log('server started'));

We can also redirect to a full URL:

const express = require('express');  
const bodyParser = require('body-parser');
const app = express();
app.use(bodyParser.json());  
app.use(bodyParser.urlencoded({ extended: true }));
app.get('/', (req, res) => {  
    res.redirect('http://google.com');  
});

app.listen(3000, () => console.log('server started'));

Then when we go to / in our browser, we get Google displayed in our browser.

We can redirect back to the referrer with:

res.redirect('back')

and we can also redirect to a higher level URL, which defaults to / .

We can use it as follows:

const express = require('express');  
const bodyParser = require('body-parser');
const app = express();  
const post = express.Router();app.use(bodyParser.json());  
app.use(bodyParser.urlencoded({ extended: true }));

post.get('/', (req, res) => {  
    res.redirect('..');  
});

app.get('/', (req, res) => {  
    res.send('hi');  
});

app.use('/post', post);app.listen(3000, () => console.log('server started'));

Then we get hi if we go to /post since we see redirect to '..' .

res.render(view [, locals] [, callback])

res.render lets us render HTML using a template. Once we set the HTML template engine, we can use template files to display the results.

The locals object has the properties that we can access in the templates.

And the callback can get the error and the rendered HTML string.

The view argument has the string with the template’s file name. The view’s folder is set before we can call res.render so we don’t need the full folder name.

For example, we can use the Pug template to render templates as follows:

const express = require('express')  
const app = express()  
app.use(express.json())  
app.use(express.urlencoded({ extended: true }))  
app.set('views', './views');  
app.set('view engine', 'pug');
app.get('/', (req, res, next) => {  
  res.render('index', { pageTitle: 'Hello', pageMessage: 'Hello there!' });  
})  
app.listen(3000, () => console.log('server started'));

Then we can add a template file called index.pug to the views folder as follows:

html  
  head  
    title= pageTitle  
  body  
    h1= pageMessage

Then we get:

https://thewebdev.info/wp-content/uploads/2020/04/hello-there.png

We can also pass in a callback to the render method as follows:

const express = require('express')  
const app = express()  
app.use(express.json())  
app.use(express.urlencoded({ extended: true }))  
app.set('views', './views');  
app.set('view engine', 'pug');app.get('/', (req, res, next) => {  
  res.render(  
    'index',  
    { pageTitle: 'Hello', pageMessage: 'Hello there!' },  
    (err, html) => {  
      if (err) {  
        next(err);  
      }  
      else {  
        console.log(html);  
      }  
    }  
  );  
})  
app.listen(3000);

Then we get the rendered HTML from the console.log :

<html><head><title>Hello</title></head><body><h1>Hello there!</h1></body></html>

Any error will be sent to the Express error handler with the next function.

Conclusion

We can render HTML results with render method.

With the redirect method, we can redirect to different paths and URLs with the different response code.

We can use the links and locations methods to send the Links and Locations response headers respectively.

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