Using Hooks in DieselJS

DieselJS allows you to enhance your request handling by utilizing hooks at various stages of the request lifecycle. Hooks enable you to execute custom logic such as logging, authentication, data manipulation, and error handling, providing a flexible and powerful way to manage your application’s behavior.

What are Hooks?

Hooks are registered with the app.addHooks method and allow you to listen to specific events in the application or request/response lifecycle our your application.

By using hooks you can interact directly with the lifecycle of diesel application. These are available hooks:

• onRequest
• preHandler
• postHandler
• onSend
• onError

onRequest

Triggered when a request is received. Ideal for logging or initial request checks. Note: -onRequest gives you req, url & server object which is enough for logging incoming request details

app.addHooks("onRequest", (req, url, server) => {
  console.log(`Request received: ${req.method} ${url}`);
  // Access the request , url and server instance here
});

preHandler

Invoked just before the request handler executes. Use this for authentication checks or data validation. preHandler only gives you context object

app.addHooks("preHandler", (ctx) => {
  // Check for authentication token
  const authToken = ctx.req.headers.get("Authorization");
  if (!authToken) {
    return new Response("Unauthorized", { status: 401 });
  }
});

postHandler

Executed after the request handler completes but before sending the response. Good for logging response data or modifying it before sending. postHandler only gives you context object

app.addHooks("postHandler", async (ctx) => {
  console.log(`Response sent for: ${ctx.req.url}`);
});

onSend

Called just before the response is sent to the client. You can manipulate the response here if necessary. onSend gives you context & result object

app.addHooks("onSend", async (ctx, result) => {
  console.log(`Sending response with status: ${result.status}`);
  return result; // Modify the response here if needed
});

onError

Executes if any error occurs during request handling. This is where you can implement centralized error logging or custom error responses. onError gives you error , request,url,server objects

app.addHooks("onError", (error, req, url, server) => {
  console.error(`Error occurred: ${error.message}`);
  // Optionally, return a new Response object or handle the error
});

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Conclusion

Using hooks in DieselJS allows for a structured and maintainable approach to managing application behavior during the request lifecycle. By strategically placing custom logic in hooks, you can streamline tasks such as logging, authentication, and error handling, leading to a more robust application architecture.