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To process and respond to requests appropriately, servers need to do more than look at a request and dispatch a response. Internally, a server needs to maintain a way to handle each request based on specific criteria such as method, pathname, etc. The process of handling requests in specific ways based on the information provided within the request is known as routing.

The method is one important piece of information that can be used to route requests. Since each HTTP request contains a method such as GET and POST, it is a great way to discern different classes of requests based on the action intended for the server to carry out. Thus, all GET requests could be routed to a specific function for handling, while all POST requests are routed to another function to be handled. This also allows for the logical co-location of processing code with the specific verb to be handled.

const server = http.createServer((req, res) => {
  const { method } = req;

  switch(method) {
    case 'GET':
      return handleGetRequest(req, res);
    case 'POST':
      return handlePostRequest(req, res);
    case 'DELETE':
      return handleDeleteRequest(req, res);
    case 'PUT':
      return handlePutRequest(req, res);
    default:
      throw new Error(`Unsupported request method: ${method}`);
  }
})

In the above example, the HTTP method property is destructured from the req object and used to conditionally invoke a handler function built specifically for handling those types of requests. This is great at first glance, but it should soon become apparent that the routing is not specific enough. After all, how will one GET request be distinguished from another?

We can distinguish one request from another of the same method through the use of the pathname. The pathname allows the server to understand what resource is being targeted. Let’s take a look at the handleGetRequest handler function.

function handleGetRequest(req, res) {
  const { pathname } = new URL(req.url);
  let data = {};

  if (pathname === '/projects') {
    data = await getProjects();
    res.setHeader('Content-Type', 'application/json');
    return res.end(JSON.stringify(data));
  }

  res.statusCode = 404;
  return res.end('Requested resource does not exist');

}

Within the handleGetRequest() function, the pathname is being checked to match a known resource, '/projects'. If the pathname matches, the resource data is fetched and then subsequently dispatched from the server as a successful response. Otherwise, the .statusCode property is set to 404, indicating that the resource is not found, and a corresponding error message is dispatched. This pattern can be extrapolated to any number of conditional resource matches, allowing the server to handle many different types of requests to different resources.

Instructions

Our server is going to handle different types of requests. Using a switch statement, add a condition to match for incoming GET requests within the callback function of .createServer().

Let’s create a handler function for the GET requests that will be received. Using the ES6 arrow function notation, assign a function to a const variable called handleGetRequest. This function should take two arguments—req and res.

Now that we have a simple handler function, we can invoke it when GET requests are received. Return the handleGetRequest() function when HTTP method matches GET. Pass the req and res variables from the .createServer() callback into the handler function as the first and second arguments, respectively.

Now that we can handle GET requests, let’s turn our attention to the resource for which the GET request is being made. This distinction can be made using the pathname. Within the handleGetRequest() function, create a const variable called pathname, assigning it the value of the url from the request. Then, write an if statement to match the pathname of '/users'.

In the if statement that you just created, return an empty array as a response. Use the JSON.stringify() method to convert the array into a JSON string.

Run your code with node app.js, then click on the “Check Work” button.

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