84 lines
2.7 KiB
Markdown
84 lines
2.7 KiB
Markdown
---
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tags:
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- Programming_Languages
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- backend
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- node-js
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- node-modules
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---
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The HTTP Module allows us to create a web server that listens for HTTP requests on a given port. It is therefore perfect for creating backends for client-side JavaScript.
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## Creating a server
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An HTTP server is another instance of an [event emitter](Events%20module.md#event-emitters). It therefore has all the same methods as the `EventEmitter` class: `on`, `emit`, `addListener` etc. This demonstrates again how much of Node's core functionality is based on event emitters.
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*Creating a server*
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````js
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const http = require('http')
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const server = http.createServer() // Create server as emitter
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// Register functions to run when listener listener is triggered
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server.on('connection', (socket) => {
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console.log('new connection...')
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})
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server.listen(3000)
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console.log('Listening on port 3000')
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````
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This server is functionally equivalent to a generic event emitter:
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````js
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// Raise an event
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const emitter = new EventEmitter('messageLogged')
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// Register a listener
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emitter.on('messagedLogged', function() {
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console.log('The listener was called.')
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})
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````
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Whenever a request is made to this server, it raises an event. We can therefore target it with the `on` method and make it execute a function when requests are made.
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If we were to start the server by running the file and we then used a browser to navigate to the port, we would see `new connection` logged every time we refresh the page.
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### Sockets and `req, res`
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A socket is a generic protocol for client-server communication. Crucially it allows simultaneous communication both ways. The client can contact the server but the server can also contact the client. Our listener function above uses a socket as the callback function but in most cases this is quite low-level, not distinguishing responses from requests. It is more likely that you would initiate a `request, resource` architecture in place of a socket:
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````js
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const server = http.createServer((req, res) => {
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if (req.url === '/'){
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res.write('hello')
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res.end()
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}
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})
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````
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#### Return JSON
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Below is an example of using this architecture to return JSON to the client:
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````js
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const server = http.createServer((req, res) => {
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if (req.url === '/products'){
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res.write(JSON.stringify(['shoes', 'lipstick', 'cups']))
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res.end()
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}
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})
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````
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### Express
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In reality you would rarely use the `http` module directly to create a server. This is because it is quite low level and each response must be written in a linear fashion as with the two URLs in the previous example. Instead we use Express which is a framework for creating servers and routing that is an abstraction on top of the core HTTP module.
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* [Create RESTful API with Express](Create%20RESTful%20API%20with%20Express.md)
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