#Cloudflare Workers - Debugging

How can we debug errors in our Cloudflare Workers functions?

Let's imagine that we have deployed the following code as a Cloudflare Worker function using Serverless:

addEventListener('fetch', (event) => {
  event.respondWith(handleRequest(event.request));
});
async function handleRequest(request) {
  const answer = request.headers.get('greeting') || 'hello';
  return new Response(answer + ' world');
}

And its corresponding Serverless yml file:

# serverless.yml
---
functions:
  helloWorld:
    # What the script will be called on Cloudflare (this property value must match the function name one line above)
    name: helloWorld
    # The name of the script on your machine, omitting the .js file extension
    script: helloWorld
    events:
      - http:
          url: example.com/hello/user
          # Defines the method used by serverless when the `invoke` command is used. Cloudflare Workers only support GET requests for now
          method: GET
          headers:
            greeting: hi

Let's invoke correctly that function

serverless invoke --function helloWorld

# Output
hi world

If we were to call the above function without any headers, you would get hello world back instead of hi world, so we know that our worker is properly reading the greeting header.

#Cloudflare Workers Playground

Cloudflare Workers also have a Playground you can use to modify a Cloudflare Worker and see the results live on the same screen. The Cloudflare Workers Playground is another great way to debug your worker.