1. Introduction

In this tutorial, we will explore how to utilize getInitialProps for efficient data population when working with Next.js. This function allows us to fetch data before our page is rendered, a crucial step in creating fast, dynamic web applications.

By the end of this tutorial, you will be able to:
- Understand the purpose and functionality of getInitialProps
- Implement getInitialProps in your Next.js application
- Fetch data before rendering your page

Prerequisites:
- Basic understanding of JavaScript and React.js
- Familiarity with Next.js is beneficial, but not necessary

2. Step-by-Step Guide

getInitialProps is an async static method introduced by Next.js. It allows us to populate our initial component props before the rendering process begins. This is especially useful when you need to fetch some data from an API and use it in your component as props.

Using getInitialProps

In your page-level component, you can define getInitialProps and it will be executed before the page render. The result from getInitialProps will be serialized when server rendering, allowing for automatic state hydration.

Note that getInitialProps can only be added to the default component exported by a page. You cannot use it with regular components.

3. Code Examples

Let's create a simple Next.js application that fetches some user data from an API before rendering.

Example 1: Fetching data with getInitialProps

import fetch from 'isomorphic-unfetch';

const UserProfile = (props) => (
  <div>
    <h1>{props.user.name}</h1>
    <p>{props.user.email}</p>
  </div>
);

UserProfile.getInitialProps = async function(context) {
  const { id } = context.query;
  const res = await fetch(`https://api.example.com/user/${id}`);
  const user = await res.json();

  return { user };
};

export default UserProfile;

Here's a breakdown of the code:

• We're using the isomorphic-unfetch module to fetch data, which works both on the client and server.
• The UserProfile component is defined, which receives props and renders user information.
• getInitialProps is defined as an async function. It receives a single argument, context, which is an object with various properties useful for fetching data.
• Within getInitialProps, we fetch the user data from an API and return it as props to the UserProfile component.

4. Summary

In this tutorial, we've learned about getInitialProps and how it can be used to populate initial component props in a Next.js application. We've also gone through a practical example of fetching data before rendering our page.

For further learning, you can explore more about data fetching techniques in Next.js, such as getServerSideProps and getStaticProps, which are more suitable for new Next.js projects.

5. Practice Exercises

Exercise 1:
Create a Next.js application that fetches a list of posts from the JSONPlaceholder API and displays their titles.

Exercise 2:
Modify the above application to show the content of a post when its title is clicked. Fetch the post data using getInitialProps.

Exercise 3:
Create an application that fetches and displays user data from an API. The application should have two pages: a user list and a user detail page. Use getInitialProps to fetch the data.

Remember to experiment and practice as much as possible to get a solid understanding of using getInitialProps in Next.js. Happy coding!