Calling external APIs from Edge Functions in Supabase - Mini Project: Build & Apply

Calling external APIs from Edge Functions

📖 Scenario: You are building a small cloud function that runs at the edge. This function will call an external API to get some data and then return it. Edge Functions run close to users for fast response.

🎯 Goal: Create an Edge Function in Supabase that calls the external API https://api.agify.io?name=michael to get the predicted age for the name 'michael'. You will set up the function, configure the API URL, fetch the data, and return the JSON response.

📋 What You'll Learn

Create a variable with the external API URL

Add a configuration variable for the name parameter

Write the fetch call to get data from the API

Return the JSON response from the Edge Function

💡 Why This Matters

🌍 Real World

Edge Functions are used to run code close to users for fast responses. Calling external APIs lets you enrich your functions with live data from other services.

💼 Career

Many cloud jobs require writing serverless functions that integrate with external APIs. This project teaches the basics of that important skill.

1

Set up the API URL variable

Create a variable called apiUrl and set it to the string "https://api.agify.io?name=michael".

Supabase

// Create a variable called apiUrl with the external API URL
// Your code here

Hint

Use const apiUrl = "https://api.agify.io?name=michael"; to store the API URL.

2

Add a configuration variable for the name

Create a variable called name and set it to the string "michael". Then update apiUrl to use this name variable in the URL with template literals.

Supabase

const apiUrl = `https://api.agify.io?name=michael`;
// Create a variable called name with value "michael" and update apiUrl to use it
// Your code here

Hint

Use const name = "michael"; and template literals like `https://api.agify.io?name=${name}`.

3

Fetch data from the external API

Write an async function called handler that fetches data from apiUrl using fetch. Await the response and then await response.json() to get the data.

Supabase

const name = "michael";
const apiUrl = `https://api.agify.io?name=${name}`;

// Write an async function handler that fetches from apiUrl and gets JSON data
// Your code here

Hint

Use export async function handler() and inside it const response = await fetch(apiUrl); then const data = await response.json();.

4

Return the JSON response from the Edge Function

In the handler function, return a new Response object with the JSON stringified data and set the header Content-Type to application/json.

Supabase

const name = "michael";
const apiUrl = `https://api.agify.io?name=${name}`;

export async function handler() {
  const response = await fetch(apiUrl);
  const data = await response.json();
  // Return the JSON response with proper headers
  // Your code here
}

Hint

Use return new Response(JSON.stringify(data), { headers: { "Content-Type": "application/json" } }); to return JSON properly.

Practice

1. What is the main purpose of using fetch in Supabase Edge Functions when calling external APIs?

easy

A. To create user interface components

B. To store data permanently in Supabase database

C. To run SQL queries inside the Edge Function

D. To send requests and receive data from external services

Solution

1. Step 1: Understand the role of fetch in Edge Functions

   fetch is used to send HTTP requests to external APIs and get responses back.

2. Step 2: Identify what fetch does not do

   It does not store data permanently or create UI components; it only communicates with external services.

3. Final Answer:

   To send requests and receive data from external services -> Option D

4. Quick Check:

   fetch calls external APIs = C [OK]

Hint: Remember: fetch is for talking to outside services [OK]

Common Mistakes:

• Thinking fetch stores data permanently
• Confusing fetch with database queries
• Assuming fetch creates UI elements

2. Which of the following is the correct syntax to call an external API using fetch inside a Supabase Edge Function?

easy

A. const response = fetch('https://api.example.com/data').then(res => res.json())

B. const response = fetch.get('https://api.example.com/data')

C. const response = fetch('https://api.example.com/data')

D. const response = fetch('https://api.example.com/data').json()

Solution

1. Step 1: Recall the correct usage of fetch

   fetch returns a promise; to get JSON data, you call then(res => res.json()).

2. Step 2: Check each option for syntax correctness

   const response = fetch('https://api.example.com/data') misses handling the promise; B uses invalid method; D incorrectly calls json() directly on fetch.

3. Final Answer:

   const response = fetch('https://api.example.com/data').then(res => res.json()) -> Option A

4. Quick Check:

   fetch + then(res.json()) = A [OK]

Hint: Always handle fetch with then() or await for JSON [OK]

Common Mistakes:

• Calling json() directly on fetch without then or await
• Using fetch.get which does not exist
• Ignoring the promise returned by fetch

3. Consider this Edge Function code snippet:

export async function handler() {
  const response = await fetch('https://api.example.com/data');
  const data = await response.json();
  return new Response(JSON.stringify({ result: data.value }), { status: 200 });
}

If the external API returns { "value": 42 }, what will the Edge Function return?

medium

A. An error because data.value is undefined

B. A response with body '{"result":42}' and status 200

C. A response with body '42' and status 404

D. A response with body '{"value":42}' and status 200

Solution

1. Step 1: Understand the API response and parsing

   The API returns JSON {"value": 42}, which is parsed into data object with data.value = 42.

2. Step 2: Check the returned response from the Edge Function

   The function returns JSON string with key "result" and value data.value (42), status 200.

3. Final Answer:

   A response with body '{"result":42}' and status 200 -> Option B

4. Quick Check:

   API value 42 mapped to result key = D [OK]

Hint: Map API data correctly before returning JSON [OK]

Common Mistakes:

• Returning original API JSON without mapping
• Confusing status codes
• Assuming data.value is undefined

4. You wrote this Edge Function code to call an external API:

export async function handler() {
  const response = fetch('https://api.example.com/data');
  const data = await response.json();
  return new Response(JSON.stringify(data), { status: 200 });
}

What is the main error in this code?

medium

A. Missing await before fetch causing response to be a Promise

B. Using await on response.json() is incorrect

C. Response constructor cannot take JSON string

D. The function should not return a Response object

Solution

1. Step 1: Identify how fetch is called

   fetch returns a Promise, so it must be awaited to get the response object.

2. Step 2: Check usage of await on response.json()

   Awaiting response.json() is correct; the error is missing await on fetch.

3. Final Answer:

   Missing await before fetch causing response to be a Promise -> Option A

4. Quick Check:

   Missing await before fetch causing response to be a Promise = B [OK]

Hint: Always await fetch before calling response methods [OK]

Common Mistakes:

• Not awaiting fetch before response.json()
• Thinking response.json() does not need await
• Misunderstanding Response constructor usage

5. You want to call two different external APIs sequentially inside a Supabase Edge Function and combine their results before returning. Which code snippet correctly does this?

hard

A. const [res1, res2] = await Promise.all([
fetch('https://api1.com/data'),
fetch('https://api2.com/data')
]);
const data1 = await res1.json();
const data2 = await res2.json();
return new Response(JSON.stringify({ first: data1, second: data2 }), { status: 200 });

B. const res1 = fetch('https://api1.com/data');
const data1 = await res1.json();
const res2 = fetch('https://api2.com/data');
const data2 = await res2.json();
return new Response(JSON.stringify({ first: data1, second: data2 }), { status: 200 });

C. const res1 = await fetch('https://api1.com/data');
const data1 = await res1.json();
const res2 = await fetch('https://api2.com/data');
const data2 = await res2.json();
return new Response(JSON.stringify({ first: data1, second: data2 }), { status: 200 });

D. const data1 = fetch('https://api1.com/data').json();
const data2 = fetch('https://api2.com/data').json();
return new Response(JSON.stringify({ first: data1, second: data2 }), { status: 200 });

Solution

1. Step 1: Understand sequential API calls

   To call APIs one after another, await each fetch and parse before next call.

2. Step 2: Check each option for correct async handling

   const res1 = await fetch('https://api1.com/data'); const data1 = await res1.json(); const res2 = await fetch('https://api2.com/data'); const data2 = await res2.json(); return new Response(JSON.stringify({ first: data1, second: data2 }), { status: 200 }); correctly awaits each fetch and json parsing sequentially. const res1 = fetch('https://api1.com/data'); const data1 = await res1.json(); const res2 = fetch('https://api2.com/data'); const data2 = await res2.json(); return new Response(JSON.stringify({ first: data1, second: data2 }), { status: 200 }); misses await on fetch. const [res1, res2] = await Promise.all([ fetch('https://api1.com/data'), fetch('https://api2.com/data') ]); const data1 = await res1.json(); const data2 = await res2.json(); return new Response(JSON.stringify({ first: data1, second: data2 }), { status: 200 }); uses parallel calls, not sequential. const data1 = fetch('https://api1.com/data').json(); const data2 = fetch('https://api2.com/data').json(); return new Response(JSON.stringify({ first: data1, second: data2 }), { status: 200 }); incorrectly calls json() directly.

3. Final Answer:

   const res1 = await fetch('https://api1.com/data');\nconst data1 = await res1.json();\nconst res2 = await fetch('https://api2.com/data');\nconst data2 = await res2.json();\nreturn new Response(JSON.stringify({ first: data1, second: data2 }), { status: 200 }); -> Option C

4. Quick Check:

   Sequential await fetch + json = A [OK]

Hint: Await each fetch and json call in order for sequential calls [OK]

Common Mistakes:

• Not awaiting fetch before json()
• Calling json() directly on fetch
• Mixing parallel and sequential calls incorrectly