Calling external APIs from Edge Functions in Supabase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to fetch data from an external API using fetch.

Supabase

const response = await fetch([1]);
const data = await response.json();

Drag options to blanks, or click blank then click option'

A'https://api.example.com/data'

Bapi.example.com/data

Cresponse.json()

Dfetch('https://api.example.com/data')

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to put the URL in quotes

Passing the fetch call itself instead of the URL

The fetch function requires the full URL as a string to call the external API.

2fill in blank

medium

Complete the code to set the HTTP method to POST in the fetch options.

Supabase

const response = await fetch('https://api.example.com/data', {
  method: [1]
});

Drag options to blanks, or click blank then click option'

A'PUT'

B'GET'

C'POST'

D'DELETE'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'GET' instead of 'POST' when sending data

Not putting the method value in quotes

To send data to the API, the HTTP method must be set to 'POST'.

3fill in blank

hard

Fix the error in setting the request headers to send JSON data.

Supabase

const response = await fetch('https://api.example.com/data', {
  method: 'POST',
  headers: [1],
  body: JSON.stringify({ key: 'value' })
});

Drag options to blanks, or click blank then click option'

A{ 'Content-Type': application/json }

B{ Content-Type: 'application/json' }

C{ 'content-type': 'application/json' }

D{ 'Content-Type': 'application/json' }

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting the header key

Not quoting the header value

Using wrong case for 'Content-Type'

Headers must be an object with string keys and string values. The key 'Content-Type' must be quoted and the value must be a string.

4fill in blank

hard

Fill both blanks to correctly handle the fetch response and parse JSON.

Supabase

const response = await fetch('https://api.example.com/data');
const [1] = await response.[2]();

Drag options to blanks, or click blank then click option'

Adata

Bjson

Ctext

Dresult

Attempts:

3 left

💡 Hint

Common Mistakes

Using response.text() instead of response.json()

Not awaiting the response parsing

The response object has a method json() to parse the response body as JSON. We store the result in a variable, commonly named 'data'.

5fill in blank

hard

Fill all three blanks to send a POST request with JSON body and handle the response.

Supabase

const response = await fetch([1], {
  method: [2],
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ message: 'Hello' })
});
const result = await response.[3]();

Drag options to blanks, or click blank then click option'

A'https://api.example.com/send'

B'POST'

Cjson

D'GET'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'GET' instead of 'POST' for sending data

Not quoting the URL or method

Parsing response with text() instead of json()

To send data, use the POST method and the correct URL. Then parse the response with response.json().

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