ReactJS

Understanding Next.js Data Fetching for Beginners

Published May 9, 2022

Updated Feb 13, 2023

4 min read

This article was written over 18 months ago and may contain information that is out of date. Some content may be relevant but please refer to the relevant official documentation or available resources for the latest information.

When I started to learn Next.Js, I felt a little bit lost with some abbreviations they use to make the data fetching. All of them look pretty simmilar, but they have different meanings. If you feel the same, you are not alone. Let's discover what CSR, SSR, SSG, and ISR means, and how we can use them.

It is quite confusing because I, as an Angular developer, only knew one strategy to fetch the data:HttpClient. But for example, if you are more familiar with React, you probably use a different strategy: useEffect.

So, let's get started. Vercel's Next.js framework has four different data fetching options despite being known as a server-side render framework:

CSR - Client-Side Rendering is a common data fetching method using useEffect. It will fetch the data from the API every single page request on the client-side (after the page is rendered, then the function will run).
SSR - Server-Side Rendering will run a special function to fetch data from the API with every page request on the server-side (before the page is loaded, that special function will run first, creating a delay, then after that, it will serve the page).
SSG - Static Site Generation will run a special function to fetch data once when that page builds.
ISR – Incremental Static Regeneration offers a new method. Shortly put, it is a combination of SSG, and SSR, where it served statically, but at a certain time and certain condition, that page will rebuild and fetch the data from the API again.

Don't worry if you don't understand any of the concepts. I will explain a little bit further shortly.

CSR (Client-Side Rendering)

This is a basic example of how you can use Client-Side Rendering. I'm using the well known useEffect method from React.

const ClientSide = () => {
  const [data, setData] = useState(null);
  const [isLoading, setLoading] = useState(false);

  useEffect(() => {
    setLoading(true);
    fetch('api/hello')
      .then((res) => res.json())
      .then((data) => {
        setData(data);
        setLoading(false);
      });
  }, []);

  if (isLoading) return <p>Loading...</p>;
  if (!data) return <p>No profile data</p>;

  return (
    <div>
      <h1>My name is {data.name}</h1>
    </div>
  );
};

export default ClientSide;

You can see how it works on Stackblitz.

We can highlight 2 things here:

The useEffect method to make the retrieve of the name every time the page loads.
A loading indicator, this is used to wait for the fetching data, because the data is fetched after the page is rendered.

SSR (Server-Side Rendering)

Just to keep in mind, when you are using Server-Side rendering, and using the method getServerSideProps(), Next.js will pre-render this page on each request using the data returned by getServerSideProps.

import styles from '../styles/Home.module.css';

const ServerSide = ({ joke }) => {
  return (
    <div className={styles.container}>
      <span className={styles.description}>Today's joke:</span>
      <h1 className={styles.title}>{joke}</h1>
    </div>
  );
};

// This gets called on every request
export async function getServerSideProps() {
  const url = 'https://icanhazdadjoke.com/';
  const res = await fetch(url, {
    headers: {
      Accept: 'application/json',
    },
  });
  const data = await res.json();

  return {
    props: {
      joke: data.joke,
    },
  };
}

export default ServerSide;

You can see how it works: Stackblitz

We had 3 highlights here:

Method getServerSideProps(), is a function indicating that a page is using Server-Side Rendering.
We had a delay before render, and NO loading indicator. The data is fetched before the page is rendered, so that's why we can see a little delay.
Data is fetched on every request, that's why every time we reload the page, is showing a different dad joke.

SSG (Static Site Generator)

If we take a look at the code below, we will see that it is pretty similar to the SSR code, but the difference here is the getStaticProps method. This method will only fetch when the app is building.

import styles from '../styles/Home.module.css';

const StaticSite = ({ joke }) => {
  console.log(joke);

  return (
    <div className={styles.container}>
      <span className={styles.description}>Today's joke:</span>
      <h1 className={styles.title}>{joke}</h1>
    </div>
  );
};

// This gets called on every request
export async function getStaticProps() {
  console.log('getStaticProps');

  const url = 'https://icanhazdadjoke.com/';
  const res = await fetch(url, {
    headers: {
      Accept: 'application/json',
    },
  });
  const data = await res.json();
  console.log(data);

  return {
    props: {
      joke: data.joke,
    },
  };
}

export default StaticSite;

The highlights here are:

getStaticProps is a method indicating that the page is using Static Site Generation.
Data will be fetched only when you run yarn build. The API will be hit only when the app is building.
Data will NOT change because there is no further fetch.

You can see how it works: Stackblitz

ISR (Incremental Static Regeneration)

This strategy works pretty simmilar like SSG, but here we need to add a revalidate prop to our main getStaticProps function.

import styles from '../styles/Home.module.css';

const IncrementalStatic = ({ joke }) => {
  console.log(joke);

  return (
    <div className={styles.container}>
      <span className={styles.description}>Today's joke:</span>
      <h1 className={styles.title}>{joke}</h1>
    </div>
  );
};

export async function getStaticProps() {
  console.log('getStaticProps');

  const url = 'https://icanhazdadjoke.com/';
  const res = await fetch(url, {
    headers: {
      Accept: 'application/json',
    },
  });
  const data = await res.json();
  console.log(data);

  return {
    props: {
      joke: data.joke,
      revalidate: 20,
    },
  };
}

export default IncrementalStatic;

There are a few keys to highlight here:

When you set the revalidate prop to certain amount of time (in our example we set it to 20), reloading doesn't trigger changes. The page will remain in a cooldown state.
Is the page rebuilt every 20 seconds then?

No. When the cooldown state is off, if no one visits the page, it will not rebuild even after the 20s pass. But the first person who enters the page when the cooldown state is off will trigger a rebuild. However, that person will not see those changes. But the changes will be applied to the next full reload.

You can see how it works: Stackblitz

Conclusion

Understand how these abbreviations work, and how we can use it in a Next.js app will help us develop more robust solutions, and use Next.js' full potential. I know these terms can sound overwhelming and difficult to understand, but with a little bit of practicing, we can see in action in a few steps.

In future blog posts, we will see the best approach to identify and choose between them.

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About the author(s)

Daian Scuarissi
@asdaian @SDaian

Exploring Angular Forms: A New Alternative with Signals

Exploring Angular Forms: A New Alternative with Signals In the world of Angular, forms are essential for user interaction, whether you're crafting a simple login page or a more complex user profile interface. Angular traditionally offers two primary approaches: template-driven forms and reactive forms. In my previous series on Angular Reactive Forms, I explored how to harness reactive forms' power to manage complex logic, create dynamic forms, and build custom form controls. A new tool for managing reactivity - signals - has been introduced in version 16 of Angular and has been the focus of Angular maintainers ever since, becoming stable with version 17. Signals allow you to handle state changes declaratively, offering an exciting alternative that combines the simplicity of template-driven forms with the robust reactivity of reactive forms. This article will examine how signals can add reactivity to both simple and complex forms in Angular. Recap: Angular Forms Approaches Before diving into the topic of enhancing template-driven forms with signals, let’s quickly recap Angular's traditional forms approaches: 1. Template-Driven Forms: Defined directly in the HTML template using directives like ngModel, these forms are easy to set up and are ideal for simple forms. However, they may not provide the fine-grained control required for more complex scenarios. Here's a minimal example of a template-driven form: ` ` 2. Reactive Forms: Managed programmatically in the component class using Angular's FormGroup, FormControl, and FormArray classes; reactive forms offer granular control over form state and validation. This approach is well-suited for complex forms, as my previous articles on Angular Reactive Forms discussed. And here's a minimal example of a reactive form: ` ` Introducing Signals as a New Way to Handle Form Reactivity With the release of Angular 16, signals have emerged as a new way to manage reactivity. Signals provide a declarative approach to state management, making your code more predictable and easier to understand. When applied to forms, signals can enhance the simplicity of template-driven forms while offering the reactivity and control typically associated with reactive forms. Let’s explore how signals can be used in both simple and complex form scenarios. Example 1: A Simple Template-Driven Form with Signals Consider a basic login form. Typically, this would be implemented using template-driven forms like this: ` ` This approach works well for simple forms, but by introducing signals, we can keep the simplicity while adding reactive capabilities: ` ` In this example, the form fields are defined as signals, allowing for reactive updates whenever the form state changes. The formValue signal provides a computed value that reflects the current state of the form. This approach offers a more declarative way to manage form state and reactivity, combining the simplicity of template-driven forms with the power of signals. You may be tempted to define the form directly as an object inside a signal. While such an approach may seem more concise, typing into the individual fields does not dispatch reactivity updates, which is usually a deal breaker. Here’s an example StackBlitz with a component suffering from such an issue: Therefore, if you'd like to react to changes in the form fields, it's better to define each field as a separate signal. By defining each form field as a separate signal, you ensure that changes to individual fields trigger reactivity updates correctly. Example 2: A Complex Form with Signals You may see little benefit in using signals for simple forms like the login form above, but they truly shine when handling more complex forms. Let's explore a more intricate scenario - a user profile form that includes fields like firstName, lastName, email, phoneNumbers, and address. The phoneNumbers field is dynamic, allowing users to add or remove phone numbers as needed. Here's how this form might be defined using signals: ` > Notice that the phoneNumbers field is defined as a signal of an array of signals. This structure allows us to track changes to individual phone numbers and update the form state reactively. The addPhoneNumber and removePhoneNumber methods update the phoneNumbers signal array, triggering reactivity updates in the form. ` > In the template, we use the phoneNumbers signal array to dynamically render the phone number input fields. The addPhoneNumber and removePhoneNumber methods allow users to reactively add or remove phone numbers, updating the form state. Notice the usage of the track function, which is necessary to ensure that the ngFor directive tracks changes to the phoneNumbers array correctly. Here's a StackBlitz demo of the complex form example for you to play around with: Validating Forms with Signals Validation is critical to any form, ensuring that user input meets the required criteria before submission. With signals, validation can be handled in a reactive and declarative manner. In the complex form example above, we've implemented a computed signal called formValid, which checks whether all fields meet specific validation criteria. The validation logic can easily be customized to accommodate different rules, such as checking for valid email formats or ensuring that all required fields are filled out. Using signals for validation allows you to create more maintainable and testable code, as the validation rules are clearly defined and react automatically to changes in form fields. It can even be abstracted into a separate utility to make it reusable across different forms. In the complex form example, the formValid signal ensures that all required fields are filled and validates the email and phone numbers format. This approach to validation is a bit simple and needs to be better connected to the actual form fields. While it will work for many use cases, in some cases, you might want to wait until explicit "signal forms" support is added to Angular. Tim Deschryver started implementing some abstractions around signal forms, including validation and wrote an article about it. Let's see if something like this will be added to Angular in the future. Why Use Signals in Angular Forms? The adoption of signals in Angular provides a powerful new way to manage form state and reactivity. Signals offer a flexible, declarative approach that can simplify complex form handling by combining the strengths of template-driven forms and reactive forms. Here are some key benefits of using signals in Angular forms: 1. Declarative State Management: Signals allow you to define form fields and computed values declaratively, making your code more predictable and easier to understand. 2. Reactivity: Signals provide reactive updates to form fields, ensuring that changes to the form state trigger reactivity updates automatically. 3. Granular Control: Signals allow you to define form fields at a granular level, enabling fine-grained control over form state and validation. 4. Dynamic Forms: Signals can be used to create dynamic forms with fields that can be added or removed dynamically, providing a flexible way to handle complex form scenarios. 5. Simplicity: Signals can offer a simpler, more concise way to manage form states than traditional reactive forms, making building and maintaining complex forms easier. Conclusion In my previous articles, we explored the powerful features of Angular reactive forms, from dynamic form construction to custom form controls. With the introduction of signals, Angular developers have a new tool that merges the simplicity of template-driven forms with the reactivity of reactive forms. While many use cases warrant Reactive Forms, signals provide a fresh, powerful alternative for managing form state in Angular applications requiring a more straightforward, declarative approach. As Angular continues to evolve, experimenting with these new features will help you build more maintainable, performant applications. Happy coding!...

Oct 4, 2024

5 mins

AngularJavaScript

Tim Neutkens, Co-Author of Next.js on the State of Next

Watch this episode! Tim Neutkens, Co-author and Tech Lead for Next.js, discusses how open source maintainers are simplifying the web, and covers the challenges faced with the current Next.js setup. Tim talks about TurboPack, a solution that optimizes bundling, improves parallelism, caching, and module graph calculations. He also talks about TurboAC, which focuses on addressing performance and compatibility issues, providing seamless transitions for Next.js users. Tim highlights the importance of efficient bundling processes to avoid excessive recompilation and discusses the updates in Next.js versions to enhance caching, rendering behavior, and client-side caching. Tim also discusses some exciting upcoming features in Next.js 15. Tim Neutkens' Socials - Twitter: @timneutkens - GitHub: timneutkens - Bluesky: timneutkens.bsky.social - Website: https://timn.tech/ Links - Vercel on Twitter, LinkedIn, Facebook, Instagram, YouTube, GitHub and Vercel's website - Next.js on Twitter, GitHub, LinkedIn, YouTube, Instagram, Facebook, official Next.js website - Turbopack on Twitter, GitHub, YouTube, LinkedIn, Instagram, Official Turbopack Docs - Webpack on GitHub, Twitter, YouTube, and Official Webpack Website Show Notes - [00:00:02] Podcast episode featuring Tim Neutkens discussing Next.js and the upcoming release of TurboPack. - [00:04:27] JavaScript bundlers evolving to handle growth. - [00:07:58] TurboPack solves Webpack limitations efficiently. - [00:12:12] Bundler compatibility for optimal app performance. - [00:16:50] Client components separated in webpack instance. Turbo pack for better parallelism and stability. Industry moving towards server-side. Feed and rollup still relevant. Collaboration between tools for future. - [00:20:57] Replacing part with roll down, similar to Webpack. Overlapping ecosystem with Avonetic Conference. Limits with unbundling and loading on demand. Cycle of building frameworks and hitting limits. History of using Webpack for client-side code. Two compiler architecture for server and client. Coordination between server and client with Webpack. - [00:25:38] Server action imports, turbo pack improves performance. - [00:30:04] Next.js is popular for websites. - [00:34:18] Chipotle using Next in Vercel, exciting improvements. - [00:38:51] Next.js 15 release candidate with changes. This episode is sponsored by Wix Studio....

Aug 7, 2024

2 mins

VercelNextJS

What's New in React 18?

Finally, we have a new version of React. Officially, React 18 is now ready to use! What new features were introduced in this version? Let’s find out in detail. In my opinion, the latest feature that revolutionized the React Ecosystem was React Hooks, introduced in React 16.8 back in 2019. Since then, we have seen many versions being released. But without any major changes, what will happen in React 18? Let’s dig into the details. New Features Concurrent React According to the official website of React, this is the major addition in React 18. With this new feature released, the devs will benefit from being able to prepare multiple versions of your UI at the same time. So, React will delegate to the dev to identify which changes are important to re-render the component. ` ` Automatic Batching With this new exciting feature, React will combine multiple setState() calls into a single re-render to improve performance. Before this, if we had multiple setState() inside of a setTimeout(), React will re-render for every state update which sometimes causes performance issues if we have larger components. You may already be familiar with this. This feature was available in React 17, but now it comes out-of-the-box. ` ` Transitions This new feature lets the dev split the state update into two categories: urgent and low priority. For some actions, like selecting in a dropdown or updating a input, you want the action to respond immediately, so now we had the possibility to distinguish between an urgent update and a non-urgent one. Updates wrapped in startTransition are handled as non-urgent, and will be interrupted if more urgent updates like clicks or keypresses come in. ` New Suspense Features Finally, we will have Suspense in the server. In the apps that are server-rendered, we will have only one Suspense API. Another cool thing is if we use Suspense in the server, we will start progressively streaming HTML. This enables selective hydration in the client. On paper, it looks awesome, but what does that mean? If you are waiting for some data on the server, React can stream HTML for the fallback, and let the user see the rest of the page. When the data is ready, the user will able to see the content HTML. This means that a single slow data source on the server will no longer hold the entire page back. New Hooks When we started this post, we mentioned that a few years ago, Hooks were the latest feature release in React. Now, React 18 will bring new Hooks: - useId : we can use this new hook to create a new identifier in the server and in the client. ` - useTransition: to create a new state update that has lower priority. ` - useDeferredValue: to update some deferred values in a controlled way (perfect for inputs, selects, etc). ` - useSyncExternalStore - useInsertionEffect IE11 not longer supported IE11 is no longer supported since React 18. If your app needs to continue bringing support to IE11, you will need to stay at React 17.x. Conclusion The most recent release from React includes some cool features like Automatic Batching or Concurrent Mode, which should improve the performance of React in the latest release. I'm really excited to see how these new features will perform in a real-life app, but they look more than promising. As we see, React 18 introduced out-of-the-box improvements, and new features that look incredible. It has cleared the way for new possibilities in React.js app development. If you want be aware of the upcoming or most recents changes, you can check out React JS Meetups....

Apr 4, 2022

3 mins

ReactJavaScriptWeb Development

Introduction to Zod for Data Validation

As web developers, we're often working with data from external sources like APIs we don't control or user inputs submitted to our backends. We can't always rely on this data to take the form we expect, and we can encounter unexpected errors when it deviates from expectations. But with the Zod library, we can define what our data ought to look like and parse the incoming data against those defined schemas. This lets us work with that data confidently, or to quickly throw an error when it isn't correct. Why use Zod? TypeScript is great for letting us define the shape of our data in our code. It helps us write more correct code the first time around by warning us if we are doing something we shouldn't. But TypeScript can't do everything for us. For example, we can define a variable as a string or a number, but we can't say "a string that starts with user_id_ and is 20 characters long" or "an integer between 1 and 5". There are limits to how much TypeScript can narrow down our data for us. Also, TypeScript is a tool for us developers. When we compile our code, our types are not available to the vanilla JavaScript. JavaScript can't validate that the data we actually use in our code matches what we thought we'd get when we wrote our TypeScript types unless you're willing to manually write code to perform those checks. This is where we can reach for a tool like Zod. With Zod, we can write data schemas. These schemas, in the simplest scenarios, look very much like TypeScript types. But we can do more with Zod than we can with TypeScript alone. Zod schemas let us create additional rules for data parsing and validation. A 20-character string that starts with user_id_? It's z.string().startsWith('user_id_').length(20). An integer between 1 and 5 inclusive? It's z.number().int().gte(1).lte(5). Zod's primitives give us many extra functions to be more specific about *exactly* what data we expect. Unlike TypeScript, Zod schemas aren't removed on compilation to JavaScript—we still have access to them! If our app receives some data, we can verify that it matches the expected shape by passing it to your Zod schema's parse function. You'll either get back your data in exactly the shape you defined in your schema, or Zod will give you an error to tell you what was wrong. Zod schemas aren't a replacement for TypeScript; rather, they are an excellent complement. Once we've defined our Zod schema, it's simple to derive a TypeScript type from it and to use that type as we normally would. But when we really need to be sure our data conforms to the schema, we can always parse the data with our schema for that extra confidence. Defining Data Schemas Zod schemas are the variables that define our expectations for the shape of our data, validate those expectations, and transform the data if necessary to match our desired shape. It's easy to start with simple schemas, and to add complexity as required. Zod provides different functions that represent data structures and related validation options, which can be combined to create larger schemas. In many cases, you'll probably be building a schema for a data object with properties of some primitive type. For example, here's a schema that would validate a JavaScript object representing an order for a pizza: ` Zod provides a number of primitives for defining schemas that line up with JavaScript primitives: string, number, bigint, boolean, date, symbol, undefined, and null. It also includes primitives void, any, unknown, and never for additional typing information. In addition to basic primitives, Zod can define object, array, and other native data structure schemas, as well as schemas for data structures not natively part of JavaScript like tuple and enum. The documentation contains considerable detail on the available data structures and how to use them. Parsing and Validating Data with Schemas With Zod schemas, you're not only telling your program what data should look like; you're also creating the tools to easily verify that the incoming data matches the schema definitions. This is where Zod really shines, as it greatly simplifies the process of validating data like user inputs or third party API responses. Let's say you're writing a website form to register new users. At a minimum, you'll need to make sure the new user's email address is a valid email address. For a password, we'll ask for something at least 8 characters long and including one letter, one number, and one special character. (Yes, this is not really the best way to write strong passwords; but for the sake of showing off how Zod works, we're going with it.) We'll also ask the user to confirm their password by typing it twice. First, let's create a Zod schema to model these inputs: ` So far, this schema is pretty basic. It's only making sure that whatever the user types as an email is an email, and it's checking that the password is at least 8 characters long. But it is *not* checking if password and confirmPassword match, nor checking for the complexity requirements. Let's enhance our schema to fix that! ` By adding refine with a custom validation function, we have been able to verify that the passwords match. If they don't, parsing will give us an error to let us know that the data was invalid. We can also chain refine functions to add checks for our password complexity rules: ` Here we've chained multiple refine functions. You could alternatively use superRefine, which gives you even more fine grained control. Now that we've built out our schema and added refinements for extra validation, we can parse some user inputs. Let's see two test cases: one that's bound to fail, and one that will succeed. ` There are two main ways we can use our schema to validate our data: parse and safeParse. The main difference is that parse will throw an error if validation fails, while safeParse will return an object with a success property of either true or false, and either a data property with your parsed data or an error property with the details of a ZodError explaining why the parsing failed. In the case of our example data, userInput2 will parse just fine and return the data for you to use. But userInput1 will create a ZodError listing all of the ways it has failed validation. ` ` We can use these error messages to communicate to the user how they need to fix their form inputs if validation fails. Each error in the list describes the validation failure and gives us a human readable message to go with it. You'll notice that the validation errors for checking for a valid email and for checking password length have a lot of details, but we've got three items at the end of the error list that don't really tell us anything useful: just a custom error of Invalid input. The first is from our refine checking if the passwords match, and the second two are from our refine functions checking for password complexity (numbers and special characters). Let's modify our refine functions so that these errors are useful! We'll add our own error parameters to customize the message we get back and the path to the data that failed validation. ` Now, our error messages from failures in refine are informative! You can figure out which form fields aren't validating from the path, and then display the messages next to form fields to let the user know how to remedy the error. ` By giving our refine checks a custom path and message, we can make better use of the returned errors. In this case, we can highlight specific problem form fields for the user and give them the message about what is wrong. Integrating with TypeScript Integrating Zod with TypeScript is very easy. Using z.infer<typeof YourSchema> will allow you to avoid writing extra TypeScript types that merely reflect the intent of your Zod schemas. You can create a type from any Zod schema like so: ` Using a TypeScript type derived from a Zod schema does *not* give you any extra level of data validation at the type level beyond what TypeScript is capable of. If you create a type from z.string.min(3).max(20), the TypeScript type will still just be string. And when compiled to JavaScript, even that will be gone! That's why you still need to use parse/safeParse on incoming data to validate it before proceeding as if it really does match your requirements. A common pattern with inferring types from Zod schemas is to use the same name for both. Because the schema is a variable, there's no name conflict if the type uses the same name. However, I find that this can lead to confusing situations when trying to import one or the other—my personal preference is to name the Zod schema with Schema at the end to make it clear which is which. Conclusion Zod is an excellent tool for easily and confidently asserting that the data you're working with is exactly the sort of data you were expecting. It gives us the ability to assert at runtime that we've got what we wanted, and allows us to then craft strategies to handle what happens if that data is wrong. Combined with the ability to infer TypeScript types from Zod schemas, it lets us write and run more reliable code with greater confidence....

Nov 15, 2024

7 mins

JavaScriptZod

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Understanding Next.js Data Fetching for Beginners

CSR (Client-Side Rendering)

SSR (Server-Side Rendering)

SSG (Static Site Generator)

ISR (Incremental Static Regeneration)

Conclusion

Daian Scuarissi

You might also like

Exploring Angular Forms: A New Alternative with Signals

Tim Neutkens, Co-Author of Next.js on the State of Next

What's New in React 18?

Introduction to Zod for Data Validation

Let's innovate together!

You might also like

Exploring Angular Forms: A New Alternative with Signals

Tim Neutkens, Co-Author of Next.js on the State of Next

What's New in React 18?

Introduction to Zod for Data Validation