ReactJS

React 18: Concurrency and Streaming SSR

Published Jul 13, 2021

Updated Feb 14, 2023

5 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This article was written over 18 months ago and may contain information that is out of date.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.

React 18

The React team just announced React 18 alpha, along with their plans for release, earlier this month. Included in that announcement is the creation of a working group to help prepare the community for the new features, nearly all of which can be gradually adopted.

Concurrency (Concurrent mode begone!)

So we finally have an answer to what we've been wondering about for the past three years! React 18 will ship with a new concurrency model, but not a completely separate concurrency "mode". Concurrency will come from a new set of features, and just happen automatically when those features are used, so it is completely optional.

createRoot will now be the way that we initialize the root of our React applications going forward as you can see here:

import * as ReactDOM from 'react-dom';
import App from 'App';

const container = document.getElementById('app');

const root = ReactDOM.createRoot(container);

root.render(<App />);

This new createRoot also enables all the new concurrent features- a subtle distinction from a "mode" 😉. This model allows you to render work and events to be interleaved together, and allows you to assign priority to various kinds of updates. This gives us better ways of keeping UI fluid and performant.

Priority

To achieve concurrency, React now uses a cooperative multitasking model which runs a single thread that can be interrupted based on priority. Interruptions happen in between rendering various components. Since the time it takes to render a component is usually very small, it provides a very granular way to interrupt when high priority work comes through.

If you'd like to read more in depth, check out this topic in the working group.

startTransition

One of the new concurrent features is startTransition, which allows us to specify updates that might be lower priority- aka "transition" updates. Specifying updates as "transition", enables urgent updates to interrupt them, allowing interactions to be more performant.

To do this, we'll use a new API:

import { startTransition } from 'react';

// Urgent: Show what was typed
setInputValue(input);

// Mark any state updates inside as transitions
startTransition(() => {
  // Transition: Show the results
  setSearchQuery(input);
});

Urgent vs Transition Updates

Urgent actions are things like clicking, hovering, scrolling, typing, or any other action where the user expect things to happen instantly as they do natively in the browser. Transition updates are more "React-centric" things like handling and managing UI state.

Currently, all updates in React 18 and below are considered urgent. The way this is worded seems to imply a future where all updates are considered transitions, and we only need to specify urgent updates. I think it was done this way to make the adoption even more gradual, because I think realistically, most updates should be transitional, not urgent. However, people need time to get used to the idea of specifying priority before everything actually gets de-prioritized.

Automatic Update Batching

A small but significant change is that now all updates are automatically batched. You may have noticed, when building React apps, that any time you put multiple setState calls next to each other in something like an event handler, React combines them into one update so that only one render occurs. However, you may have also noticed that this does not occur in things like callbacks, setTimeout, Promises, etc.

function App() {
  const [count, setCount] = useState(0);
  const [flag, setFlag] = useState(false);

  function handlePrevClick() {
	  setCount(c => c - 1);
	  setFlag(f => !f);
	  //Currently, React will only re-render once at the end (batching!)
  } 

  function handleNextClick() {
    fetchSomething().then(() => {
      // React 18 and later DOES batch these:
      setCount(c => c + 1);
      setFlag(f => !f);
      // React will only re-render once at the end (that's batching!)
    });
  }

  return (
    <div>
	    <button onClick={handlePrevClick}>Prev</button>
      <button onClick={handleNextClick}>Next</button>
      <h1 style={{ color: flag ? "blue" : "black" }}>{count}</h1>
    </div>
  );
}

flushSync

However, maybe you were relying upon that non-batching behavior! Well, there's a new API to opt-out of batching (although the team says this should be uncommon):

import { flushSync } from 'react-dom'; // Note: react-dom, not react

function handleClick() {
  flushSync(() => {
    setCounter(c => c + 1);
  });
  // React has updated the DOM by now
  flushSync(() => {
    setFlag(f => !f);
  });
  // React has updated the DOM by now
}

Streaming Server Render

Probably one of the most impactful changes in this set is now the ability for server-side rendering or SSR to be streamed to the browser, enabling partial page sections to be rendered before the entire page is ready. This should speed up the time it takes for the user to see anything on the page.

Streaming + Selective Hydration

What does this mean exactly? So first, current SSR efforts do the entire render of the HTML page, and wait until it's completely finished before sending it to the browser. The new method allows the page to be broken up into chunks using <Suspense>. Now, the server can start streaming HTML as soon as one of these chunks is ready.

Even if that HTML gets to the browser faster, it still needs to be hydrated. Previously, this was an all-or-nothing operation, requiring the entire page's JavaScript to be downloaded. Now, we can use a combination of <Suspense> and React.lazy() to achieve partial hydration as well.

If you'd like to see an example of how the server handles this, the React team put together a nice demo:

Event Replay and Priority

If that wasn't enough already, the team also found a way to prioritize hydration for user interactive sections. React will now record interactions with various parts of the page, and prioritize hydration based on what has been interacted with. This is really elegant because it lets things that the user cares about render as quickly as possible. 👏👏👏👏

Suspense is Now Very Important

These new features are all enabled entirely by the <Suspense> component. Wrapping parts of the page that may take longer to load enables their execution to be deferred while the rest of the page gets rendered, streamed, and hydrated, enabling things to be faster and quicker to interact with!

If you'd like to see an in-depth explanation, check out this topic in the working group complete with diagrams.

Conclusion

This is an extremely exciting update with lots of promise towards better performing apps and faster load times! Increased control over what gets rendered and hydrated first will lead to much better user experiences, especially on devices that struggle to load JS efficiently.

I'm very glad we will finally get an answer on concurrency "mode" too! 😂

If you're excited to try these new changes, go ahead and install the alpha:

npm install react@alpha react-dom@alpha

The React team is looking for feedback through the working group, so feel free to participate in discussions there.

I have to give lots of credit towards @swyx, who did a lot of investigation work to point out key features from the release in this thread. Check it out!

Thanks!

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About the author(s)

Hunter Miller
@hmillerdev @arthyn

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

The HTML Dialog Element: Enhancing Accessibility and Ease of Use

The HTML Dialog Element: Enhancing Accessibility and Ease of Use Dialogs are a common component added to applications, whether on the web or in native applications. Traditionally there has not been a standard way of implementing these on the web, resulting in many ad-hoc implementations that don’t act consistently across different web applications. Often, commonly expected features are missing from dialogs due to the complexity of implementing them. However, web browsers now offer a standard dialog element. Why use the dialog element? The native dialog element streamlines the implementation of dialogs, modals, and other kinds of non-modal dialogs. It does this by implementing many of the features needed by dialogs for you that are already baked into the browser. This is helpful as it reduces the burden on the developer when making their applications accessible by ensuring that user expectations concerning interaction are met, and it can also potentially simplify the implementation of dialogs in general. Basic usage Adding a dialog using the new tag can be achieved with just a few lines of code. ` However, adding the dialog alone won’t do anything to the page. It will show up only once you call the .showModal() method against it. ` Then if you want to close it you can call the .close() method on the dialog, or press the escape key to close it, just like most other modals work. Also, note how a backdrop appears that darkens the rest of the page and prevents you from interacting with it. Neat! Accessibility and focus management Correctly handling focus is important when making your web applications accessible to all users. Typically you have to move the current focus to the active dialog when showing them, but with the dialog element that’s done for you. By default, the focus will be set on the first focusable element in the dialog. You can optionally change which element receives focus first by setting the autofocus attribute on the element you want the focus to start on, as seen in the previous example where that attribute was added to the close element. Using the .showModal() method to open the dialog also implicitly adds the dialog ARIA role to the dialog element. This helps screen readers understand that a modal has appeared and the screen so it can act accordingly. Adding forms to dialogs Forms can also be added to dialogs, and there’s even a special method value for them. If you add a element with the method set to dialog then the form will have some different behaviors that differ from the standard get and post form methods. First off, no external HTTP request will be made with this new method. What will happen instead is that when the form gets submitted, the returnValue property on the form element will be set to the value of the submit button in the form. So given this example form: ` The form element with the example-form id will have its returnValue set to Submit. In addition to that, the dialog will close immediately after the submit event is done being handled, though not before automatic form validation is done. If this fails then the invalid event will be emitted. You may have already noticed one caveat to all of this. You might not want the form to close automatically when the submit handler is done running. If you perform an asynchronous request with an API or server you may want to wait for a response and show any errors that occur before dismissing the dialog. In this case, you can call event.preventDefault() in the submit event listener like so: ` Once your desired response comes back from the server, you can close it manually by using the .close() method on the dialog. Enhancing the backdrop The backdrop behind the dialog is a mostly translucent gray background by default. However, that backdrop is fully customizable using the ::backdrop pseudo-element. With it, you can set a background-color to any value you want, including gradients, images, etc. You may also want to make clicking the backdrop dismiss the modal, as this is a commonly implemented feature of them. By default, the <dialog> element doesn’t do this for us. There are a couple of changes that we can make to the dialog to get this working. First, an event listener is needed so that we know when the user clicks away from the dialog. ` Alone this event listener looks strange. It appears to dismiss the dialog whenever the dialog is clicked, not the backdrop. That’s the opposite of what we want to do. Unfortunately, you cannot listen for a click event on the backdrop as it is considered to be part of the dialog itself. Adding this event listener by itself will effectively make clicking anywhere on the page dismiss the dialog. To correct for this we need to wrap the contents of the dialog content with another element that will effectively mask the dialog and receive the click instead. A simple element can do! ` Even this isn’t perfect though as the contents of the div may have elements with margins in them that will push the div down, resulting in clicks close to the edges of the dialog to dismiss it. This can be resolved by adding a couple of styles the the wrapping div that will make the margin stay contained within the wrapper element. The dialog element itself also has some default padding that will exacerbate this issue. ` The wrapping div can be made into an inline-block element to contain the margin, and by moving the padding from the parent dialog to the wrapper, clicks made in the padded portions of the dialog will now interact with the wrapper element instead ensuring it won’t be dismissed. Conclusion Using the dialog element offers significant advantages for creating dialogs and modals by simplifying implementation with reasonable default behavior, enhancing accessibility for users that need assistive technologies such as screen readers by using automatic ARIA role assignment, tailored support for form elements, and flexible styling options....

Oct 25, 2024

4 mins

HTMLJavaScript

What Can You Do with Tailwind 2?

What Can You Do with Tailwind 2? Tailwind CSS finally announced it's new 2.0 version on November 18th, 2020. If you've been around the industry lately, you've probably heard of Tailwind CSS, because they seem to be everywhere! But maybe you haven't, and in that case, it's time for a short introduction. If you have, skip to 2.0 Features Intro to Tailwind CSS Something that started out as some handcrafted CSS used personally by Adam Wathan became an extremely popular, productivity-boosting CSS framework used by millions over the last three years. The core mindset behind Tailwind is that CSS should be composed of small single-purpose utility classes which pull from a standard set of values. At first you may think, "This seems like inline styles, why would I want to bloat my markup and aren't those bad anyway?", and while your statement about inline styles is correct, Tailwind's utility classes aren't that at all. Here's why: 1. By sticking with only classes, styles all stay at the same specificity. 2. By using classes instead of inline styles, we encourage reuse and ensure that we're sticking to a standard set of values. 3. While our markup may be larger than those who use other CSS methodologies, we always know exactly what styles are coming from our classes because there is a 1-to-1 mapping. 4. The breadth of utility classes allows us to write 95-100% of our CSS using just utilities. This encourages a small footprint and very little maintenance overhead. There are other benefits like increased authoring speed and others that I'd like to cover in a more thorough post later. In case you're wondering, what does this look like? Here's an example component from Tailwind's homepage: Now that you've gotten a short introduction, let's get back to why we're here. 2.0 Features Since this is a major version, it needed a major launch which included not only a teaser and trailer, but also a whole new website and docs! If this isn't maximalist launching, I don't know what is! Let's see the most exciting changes with a few examples that you couldn't make without customizing version 1. Theming and Design I don't think it would be a major version launch if Tailwind didn't touch these two topics because they are the main pillars of why we use Tailwind in the first place. They didn't just touch these though, they brought big changes. Colors With regards to theming and design, the biggest of change is colors. The Tailwind team created an all new color palette which includes 17 colors and 5 grays. This is a huge jump in expressiveness for designs, especially with alternate grays because the old gray was on the cool side. The new sets add two cooler grays and two warmer grays so you can have something that jives better with your design's palette. Color docs Dark Mode Another big change is the new support for dark mode. Tailwind doesn't force one color to another for dark mode, but instead let's you control which colors get applied through the new modifier dark:. This will apply whatever style follows whenever a .dark class is above it. Dark Mode docs New Breakpoint and Extended Scales In an effort to support even more refined designs, the team has added support for a larger breakpoint 2xl which now allows more specification for larger layouts. I often added this as a custom breakpoint. Breakpoint docs They also added extended scales for spacing, typography, and opacity. For spacing, a few half values were added near the bottom for nudging smaller spacing layouts. For typography, a few values were added to the top end for larger hero text. Opacity had the largest set of adds with steps every 10, and a few half steps at the ends. Spacing, typography, and opacity docs. A Practical Look at New Theming Changes I've put together a small demo of landing page hero to show off the new changes. Try toggling the dark class to see dark mode: New and Extended Utilities It wouldn't be Tailwind without utilities, and in a major launch, we're going to see some new ones. I think both the new forms plugin and ring utilities are big wins for accessibility because they encourage good practice. The new colors are sure to help us get good contrast! Forms Forms have always been a struggle to style. We often resort to hacks and custom implementations with Javascript to be able to make them look good and match our designs. The Tailwind team has worked hard to make standard HTML form inputs able to be styled without custom elements or hacks. There are some limitations here, but I think the result looks great. Forms plugin docs Ring Another issue that we often encounter when auditing the accessibility of our apps is showing clear focus indicators. The default web version of this is accomplished through the outline property. Unfortunately, outline ignores border-radius and isn't quite as customizable as something like box-shadow. The new ring utility will use box-shadow and that will work alongside the standard shadow utilities in Tailwind without overriding them. Our focus indicators can now look as good as the rest of our UI! 💅 Ring docs Text Overflow A small change, but still helpful: you can now specify overflow-ellipsis and overflow-clip to control text overflow in a multi-line scenario. Text-overflow docs Default Line-heights Something that I feel I'm always tweaking is line-height. I think good line-heights can make or break type styles. In an effort to help improve the quality of typography in Tailwind, the team has shipped default line-heights for each text size, and like always, you can change that with the leading utility. Font-size docs Practical Example of New Utilities I've put together a small form component to show off the new utilities: Internal Mechanics Changes Quite a few internal changes have taken place, one major one being that Tailwind dropped support for IE11 in 2.0. Given that IE11 has very little representation globally and is officially unsupported by Microsoft, I think this was a good move, especially because it allows them to do even more with the framework. In addition, @apply can now work with all variants which is a huge boost to anyone who heavily used it. Previously, you were required to implement those variants as you would normal CSS, but no longer! Two things changed with config. You can easily extend variant's by adding an extend property to your variants config object. This allows you to just add new variants without having to list out all of the default variants which is just a lot nicer. The other new thing in config is that we can now set default transition timings and easing functions. This allows us to no longer need to specify a duration or easing function if we're just fine with the default, which is probably 80% of the time for me personally. @apply, variant, and transition docs The Road to 2.0 Whether you already use Tailwind or you just got converted above, there's a lot to be excited about with version 2.0. A ton of work went into it and it shows in the quality of what was launched. Creating and maintaining Tailwind quickly became the work of a small company, unfortunately Adam is only so powerful 🤣. He and Steve Schoger needed extra help which they found this year using funds made from their launch of TailwindUI and RefactoringUI. They hired Brad Cornes, Robin Malfait, and Simon Vrachliotis to assist with developing the entire ecosystem that surrounds Tailwind and to push out this new version. The team's desires for the new version were deliberated at length over many of Adam's tweets, Github issues/discussions, and even podcast episodes from Adam's very own Full Stack Radio. Something especially important to point out is the team's desire to stick to semantic versioning. Creating a new version opens up a lot of doors for change which is great, but that door also closes at the same time. Now the Tailwind team has to wait until 3.0 to make changes that will break, but I think they made good calls on what to include in this version. What's Next? If you're as excited as I am, you can head straight to this upgrade guide to dig through what changes you might need to make in your current Tailwind codebase. If you'd like to hear more straight from the creators themselves head on over to their announcement blog post to get an in-depth look at each change. For some of us, it might not be time to change and that's ok. The current version is still a serious piece of craftsmanship with all the same well-thought features. Version 1.9 will be the last update in version one and will retain support for IE11. I think Tailwind has proved to be more future-thinking than most frameworks to date including frameworks in other languages. Their attention to detail and quest for excellence shows up in the quality of their work. As a company, they're just getting started. Hopefully the future holds even more new innovations in this lovely little CSS framework, and beyond!...

Nov 24, 2020

7 mins

Tailwind CSSCSSRelease

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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React 18: Concurrency and Streaming SSR

React 18

Concurrency (Concurrent mode begone!)

Priority

startTransition

Urgent vs Transition Updates

Automatic Update Batching

flushSync

Streaming Server Render

Streaming + Selective Hydration

Event Replay and Priority

Suspense is Now Very Important

Conclusion

Hunter Miller

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