Edge Functions

What Are Edge Functions?

Think of edge functions as mini-programs that live on the internet. Instead of running on your laptop or a single server, they run on servers spread around the world, close to wherever your users are. When someone visits your app from Tokyo, the edge function runs in Tokyo. From London? It runs in London. This makes everything faster.

You do not manage servers, install software, or worry about scaling. You write a small function, deploy it with one command, and it is available to the whole world instantly. You only pay when someone actually uses it.

Deno vs. Node.js: Why Supabase Chose Deno

Deno is a modern JavaScript/TypeScript runtime — the engine that runs your code on the server. If you have heard of Node.js, Deno is its newer, more secure sibling. Supabase chose Deno for three reasons:

Challenge 1: Hello World

Every API you have ever used — weather apps, payment systems, social media feeds — works by sending and receiving JSON responses. This first challenge teaches you the most fundamental skill in backend development: making a function that responds when someone calls it.

// The simplest possible edge function
// Deno.serve is the modern way to create an HTTP server in Deno
Deno.serve(async (req) => {
  return new Response(
    JSON.stringify({ message: "Hello from the edge!" }),
    { headers: { "Content-Type": "application/json" } }
  )
})

# Deploy to Supabase
supabase functions deploy hello --project-ref <your-ref>

# Test it
curl https://<your-ref>.supabase.co/functions/v1/hello
# → {"message":"Hello from the edge!"}

Challenge 2: JSON API (Read User Input)

Challenge 1 always returned the same thing. Real APIs need to read what the user sends and respond differently. This is how login forms, search bars, and checkout buttons work — your frontend sends data, and your edge function processes it.

Deno.serve(async (req) => {
  // Parse the JSON body from the incoming request
  const { name } = await req.json()

  // Return a personalized greeting
  return new Response(
    JSON.stringify({
      greeting: `Hello, ${name}! Welcome to the edge.`
    }),
    { headers: { "Content-Type": "application/json" } }
  )
})

curl -X POST https://<ref>.supabase.co/functions/v1/greet \
  -H "Content-Type: application/json" \
  -d '{"name": "Alex"}'
# → {"greeting":"Hello, Alex! Welcome to the edge."}