nodeWebService.md

Node web service

With JavaScript we can write code that listens on a network port (e.g. 80, 443, 3000, or 8080), receives HTTP requests, processes them, and then responds. We can use this to create a simple web service that we then execute using Node.js.

First create your project.

➜ mkdir webservicetest
➜ cd webservicetest
➜ npm init -y

Now, open VS Code and create a file named index.js. Paste the following code into the file and save.

const http = require('http');
const server = http.createServer(function (req, res) {
  res.writeHead(200, { 'Content-Type': 'text/html' });
  res.write(`<h1>Hello Node.js! [${req.method}] ${req.url}</h1>`);
  res.end();
});

server.listen(8080, () => {
  console.log(`Web service listening on port 8080`);
});

This code uses the Node.js built-in http package to create our HTTP server using the http.createServer function along with a callback function that takes a request (req) and response (res) object. That function is called whenever the server receives an HTTP request. In our example, the callback always returns the same HTML snippet, with a status code of 200, and a Content-Type header, no matter what request is made. Basically this is just a simple dynamically generated HTML page. A real web service would examine the HTTP path and return meaningful content based upon the purpose of the endpoint.

The server.listen call starts listening on port 8080 and blocks until the program is terminated.

We execute the program by going back to our console window and running Node.js to execute our index.js file. If the service starts up correctly then it should look like the following.

➜ node index.js
Web service listening on port 8080

You can now open your browser and point it to localhost:8080 and view the result. The interaction between the JavaScript, node, and the browser looks like this.

Use different URL paths in the browser and note that it will echo the HTTP method and path back in the document. You can kill the process by pressing CTRL-C in the console.

Note that you can also start up Node and execute the index.js code directly in VS Code. To do this open index.js in VS Code and press the 'F5' key. This should ask you what program you want to run. Select node.js. This starts up Node.js with the index.js file, but also attaches a debugger so that you can set breakpoints in the code and step through each line of code.

Note

Make sure you complete the above steps. For the rest of the course you will be executing your code using Node.js to run your backend code and serve up your frontend code to the browser. This means you will no longer be using the VS Code Live Server extension to serve your frontend code in the browser.