Next.js 101 - Free Online Course

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Form Submission

Subscribe API endpoint

API Routes

API routes great build-in feature of Next.js.

If you need to talk to an external API, fetch data or modify data in the database, API route is the way to go.

export default (req, res) => {
  res.statusCode = 200
  res.json({ name: 'John Doe' })

Above is the default Hello API route. If you visit http://localhost:3000/api/hello in your browser, you would see the response from this endpoint.

API Response

Subscribe API Overview

Here is a quick overview of the remaining API work:

  1. send user email input from the UI
  2. create subscribe API endpoint - /api/subscribe.js
  3. subscribe API will get CONVERTKIT_API_URL, CONVERTKIT_API_KEY and CONVERTKIT_FORM_ID from env variables
  4. send request to ConvertKit API
    1. return status 201 if everything goes well
    2. return status 400 or 500 if something goes wrong
  5. Update UI accordingly
    1. While the request is pending we want to toggle the isLoading variable to true to update our UI.
    2. When the request is completed we either show a success message and error message.

Send request on form submit

When we submit a valid form, we will create a new fetch request and pass the email value in the query.

// src/components/SignupForm.js

const subscribe = async ({ email }) => {
   const res = await fetch(`/api/subscribe?email=${email}`);

// handle form submit
const onSubmit = (data) => subscribe(data);

The subscribe needs to be async/await because we need to wait for the response from the backend API.

Create Subscribe Endpoint

// src/pages/api/subscribe.js

export default (req, res) => {

   const { email, tags } = req.query;

   if (!email) {
      return res.status(400).json({ error: "Email is required" });

   // Part 2 continue


Firstly we check if the email is included in the request query. If it is not included, we will return "Email is required" error.

In the next unit we will implement the response from ConvertKit API.

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Petr Tichy
Front-end Developer

Petr is a passionate front-end developer who likes to build cool products and teach along the way.