Creating Edge Functions with Deno in Supabase - Practice Exercises

Challenge - 5 Problems

❓ service_behavior

intermediate

What is the output of this Deno Edge Function?

Consider this simple Deno Edge Function deployed on Supabase:

export async function handler(req: Request) {
  const url = new URL(req.url);
  const name = url.searchParams.get('name') || 'Guest';
  return new Response(`Hello, ${name}!`, { status: 200 });
}

What will be the response body if the function is called with the URL https://example.com?name=Alice?

Supabase

export async function handler(req: Request) {
  const url = new URL(req.url);
  const name = url.searchParams.get('name') || 'Guest';
  return new Response(`Hello, ${name}!`, { status: 200 });
}

A Hello, Alice!

B Hello, Guest!

C Error: name parameter missing

D Hello, undefined!

💡 Hint

Check how the function reads query parameters from the URL.

The function extracts the 'name' parameter from the URL query string. If it exists, it uses that value; otherwise, it defaults to 'Guest'. Since the URL has '?name=Alice', the response is 'Hello, Alice!'.

❓ Configuration

intermediate

Which option correctly configures environment variables for a Supabase Edge Function using Deno?

You want to securely access a database URL inside your Deno Edge Function on Supabase. Which configuration method correctly injects the environment variable DATABASE_URL?

A Use a global JavaScript variable declared outside the function to store the database URL.

B Pass the database URL as a query parameter in the request URL and read it inside the function.

C Set <code>DATABASE_URL</code> in the Supabase project settings under 'Environment Variables' and access it in code via <code>Deno.env.get('DATABASE_URL')</code>.

D Hardcode the database URL string directly inside the Edge Function code.

💡 Hint

Think about secure ways to handle secrets in cloud functions.

Supabase allows setting environment variables securely in project settings. Inside Deno Edge Functions, these can be accessed using Deno.env.get(). Hardcoding or passing secrets in URLs is insecure.

❓ Architecture

advanced

Which architecture best describes how Supabase Edge Functions with Deno handle incoming HTTP requests?

Supabase Edge Functions run on Deno and respond to HTTP requests. Which description best fits their architecture?

A Each HTTP request triggers a new isolated Deno runtime instance that runs the function and then shuts down immediately after responding.

B A single long-running Deno process handles all requests sequentially without isolation between them.

C Requests are queued and processed in batches by a shared Deno runtime to optimize resource usage.

D The Edge Function runs on a dedicated virtual machine that stays active 24/7 regardless of traffic.

💡 Hint

Think about how serverless functions typically run to scale efficiently.

Supabase Edge Functions run in isolated Deno runtimes per request to ensure security and scalability. Each request triggers a fresh instance that runs the function and then shuts down.

❓ security

advanced

What is the safest way to restrict access to a Supabase Edge Function?

You want only authenticated users to call your Edge Function. Which method provides the best security?

A Require users to send their username and password as query parameters to the function.

B Check the Supabase JWT token in the request headers inside the Edge Function and verify it before processing.

C Allow all requests but log the IP addresses for manual review later.

D Use a public API key hardcoded in the function code to allow access.

💡 Hint

Think about how authentication tokens work in modern web apps.

Verifying the JWT token in request headers ensures only authenticated users can access the function. Sending credentials in query parameters or hardcoding keys is insecure.

✅ Best Practice

expert

Which practice optimizes cold start performance for Supabase Edge Functions written in Deno?

Cold starts can slow down your Edge Functions. Which approach best reduces cold start latency?

A Use global variables to store user data between requests.

B Include large libraries and modules to handle all possible use cases in one function.

C Write synchronous blocking code to ensure sequential execution.

D Minimize external dependencies and keep the function code small and focused.

💡 Hint

Think about what affects startup time in serverless functions.

Smaller code and fewer dependencies reduce the time needed to start the Deno runtime, improving cold start performance. Large libraries and blocking code increase latency. Global variables do not persist between invocations.