Xano’s custom middleware is a nifty way to add reusable logic to your API requests. Let’s walk through how to create and use custom middleware in Xano for processing API requests.

1. First, log in to your Xano dashboard.
2. Head over to the "Add-ons" section by clicking it on the left sidebar.
3. In the "Add-ons" section, find and click on the "Middleware" tab.

1. Click the “Create New Middleware” button.
2. Give it a name and, if you want, add a description to explain what the middleware does.
3. Hit “Save” to create your new middleware template.

1. After creating the middleware, click on its name in the list to open the editor.
2. Define your logic using JavaScript in the provided code editor.

• Implement functions like before(), after(), and onError().
  • before(): Code that runs before the request goes to the backend.
  • after(): Code that runs after getting a response from the backend but before sending it back to the client.
  • onError(): Code to handle any errors that pop up during the process.

1. Use the ctx object to interact with the request and response context.

Example:

function before(ctx) {
    // Add a custom header
    ctx.request.headers['custom-header'] = 'CustomValue';
}

function after(ctx) {
    // Modify response data
    ctx.response.body.timestamp = Date.now();
}

function onError(err, ctx) {
    // Log error or modify error response
    console.error(err);
    ctx.response.body.error_message = "An unexpected error occurred.";
}

1. Save your middleware code.

1. Go to the “API” section from the left sidebar.
2. Pick the API you want to apply the middleware to.
3. Under the selected API, choose the specific endpoint you want to attach the middleware to.
4. In the endpoint editor, find the “Middleware” section.
5. Click “Add Middleware” and select your custom middleware from the list.
6. Save your changes.

1. Use Xano’s built-in API testing tools or any external tools (like Postman) to send requests to the API endpoint where the middleware is applied.
2. Watch how it behaves and make sure the middleware logic works as expected.

1. If the middleware isn’t working as expected, go back to the code and debug any issues.
2. Use Xano's logging features to track the execution flow and diagnose problems.
3. Optimize middleware performance by avoiding heavy computational tasks and using asynchronous functions when needed.