Angular

Accessible Tabs in Angular

Published May 6, 2020

Updated Feb 14, 2023

4 min read

Make it Accessible - 4 Part Series

This article was written over 18 months ago and may contain information that is out of date.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

Accessible Tabs in Angular

I have written this article to guide you through the process of building a Tab interface that complies with the WAI-ARIA 1.1 Specification. I know that sounds scary, but it's much more approachable than it sounds.

The Problem

When we are working with a user interface, we often have too much content for the space available.

The Solution

We could solve the problem by dividing the big chunk of info into smaller pieces. Then, we can show a single chunk at a time, and allow users to jump between the different chunks available. Then, voila! Suddenly, we need to build a tab interface.

The Implementation

If you've been reading the Make it Accessible series, you probably know the first step. If you don't, just go to this page WAI-ARIA Practices, which is a an amazing resource for learning how to make your apps more accessible. That site is going to be your best friend from now on.

As you can see, it lists a bunch of common widgets for user interfaces. The one we're looking for is Tabs, which is under the number 3.22, or accessed directly at Tabs Section of the WAI-ARIA Practices.

The first thing to notice is that they describe the terms used:

Tabs or Tabbed Interface: A set of tab elements and their associated tab panels.
Tab List: A set of tab elements contained in a tablist element.
Tab: An element in the tab list that serves as a label for one of the tab panels and can be activated to display that panel.
Tabpanel: The element that contains the content associated with a tab.

There's also a list of Keyboard Interactions, and a few examples. Sadly, all the examples in the WAI-ARIA specification are in plain HTML + Javascript. That's why I decided to start writing an article for each of the available widgets built with Angular.

Enough talk

Let's start by generating a new application. You can do that by using the Angular CLI. For this project, I'm using the version 9.0.5. Just open your terminal of choice, and type ng new ng-tabs, and the Angular CLI will take care of creating all the files you'll need for your application.

Next, we are going to generate the first module named SharedModule. For this, we'll go back to the Angular CLI. While in your terminal of choice, go to the project's folder, and type ng g module shared. It will generate the module for you. You'll then need to import it in your src/app/app.module.ts file like this:

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppRoutingModule } from './app-routing.module';
import { AppComponent } from './app.component';
import { SharedModule } from './shared/shared.module';

@NgModule({
  declarations: [AppComponent],
  imports: [BrowserModule, AppRoutingModule, SharedModule],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule {}

Thanks to the SharedModule, now we can create and export any component, and use it across the application. Let's create a component for each of the core concepts behind tabs- one for a tab (I'll call this tab trigger from now on), and one for a tabpanel.

Tab Trigger

We'll need a new component to hold each tab trigger's logic. This way, we can abstract some of the implementation details, and make it easier to use later on. To creat this component, we're going to use the Angular CLI again. Using your terminal, go to the project folder, and type ng g component shared/components/tab-trigger --style=scss --export --inlineTemplate. With that command, a new component will be generated, and will be automatically exported in the SharedModule.

Now, let's customize the new component. Open the src/app/shared/components/tab-trigger/tab-trigger.component.ts:

import { Component, Input } from '@angular/core';

@Component({
  selector: 'app-tab-trigger',
  template: `
    <button
      [id]="triggerId"
      role="tab"
      [attr.aria-controls]="panelId"
      [attr.aria-selected]="isActive"
      tabindex="-1"
    >
      <ng-content></ng-content>
    </button>
  `,
  styleUrls: ['./tab-trigger.component.scss']
})
export class TabTriggerComponent {
  @Input() isActive: boolean;
  @Input() triggerId: string;
  @Input() panelId: string;
}

And now, let's integrate the styles. Open the src/app/shared/components/tab-trigger/tab-trigger.component.scss:

button {
  position: relative;
  margin: 0;
  padding: 0.3em 0.5em 0.4em;
  border: 1px solid hsl(219, 1%, 72%);
  border-radius: 0.2em 0.2em 0 0;
  box-shadow: 0 0 0.2em hsl(219, 1%, 72%);
  overflow: visible;
  font-family: inherit;
  font-size: inherit;
  background: hsl(220, 20%, 94%);

  &:hover::before,
  &:focus::before,
  &[aria-selected='true']::before {
    position: absolute;
    bottom: 100%;
    right: -1px;
    left: -1px;
    border-radius: 0.2em 0.2em 0 0;
    border-top: 3px solid hsl(20, 96%, 48%);
    content: '';
  }

  &[aria-selected='true'] {
    border-radius: 0;
    background: hsl(220, 43%, 99%);
    outline: 0;
  }

  &[aria-selected='true']:not(:focus):not(:hover)::before {
    border-top: 5px solid hsl(218, 96%, 48%);
  }

  &[aria-selected='true']::after {
    position: absolute;
    z-index: 3;
    bottom: -1px;
    right: 0;
    left: 0;
    height: 0.3em;
    background: hsl(220, 43%, 99%);
    box-shadow: none;
    content: '';
  }

  &:hover,
  &:focus,
  &:active {
    outline: 0;
    border-radius: 0;
    color: inherit;
  }

  &:hover::before,
  &:focus::before {
    border-color: hsl(20, 96%, 48%);
  }
}

Tab Panel

We'll need a new component to hold each tab's panel, just like with the triggers. This way, we can abstract some of the implementation details, and make it easier to use later on. To create this component we're, going to use the Angular CLI again. Using your terminal, go to the project folder, and type ng g component shared/components/tab-panel --style=scss --export --inlineTemplate. With that command, a new component will be generated, and automatically exported in the SharedModule.

Now, let's customize the new component, open the src/app/shared/components/tab-panel/tab-panel.component.ts:

import { Component, Input } from '@angular/core';

@Component({
  selector: 'app-tab-panel',
  template: `
    <div
      [id]="panelId"
      role="tabpanel"
      [attr.aria-labelledby]="triggerId"
      tabindex="0"
    >
      <ng-content></ng-content>
    </div>
  `,
  styleUrls: ['./tab-panel.component.scss']
})
export class TabPanelComponent {
  @Input() panelId: string;
  @Input() triggerId: string;
}

And now, let's integrate the styles. Open the src/app/shared/components/tab-panel/tab-panel.component.scss:

[role='tabpanel'] {
  position: relative;
  z-index: 2;
  padding: 0.5em 0.5em 0.7em;
  border: 1px solid hsl(219, 1%, 72%);
  border-radius: 0 0.2em 0.2em 0.2em;
  box-shadow: 0 0 0.2em hsl(219, 1%, 72%);
  background: hsl(220, 43%, 99%);
}

[role='tabpanel']:focus {
  border-color: hsl(20, 96%, 48%);
  box-shadow: 0 0 0.2em hsl(20, 96%, 48%);
  outline: 0;
}

[role='tabpanel']:focus::after {
  position: absolute;
  bottom: 0;
  right: -1px;
  left: -1px;
  border-bottom: 3px solid hsl(20, 96%, 48%);
  border-radius: 0 0 0.2em 0.2em;
  content: '';
}

[role='tabpanel'] p {
  margin: 0;
}

[role='tabpanel'] * + p {
  margin-top: 1em;
}

Finish it

All we have left is to use our new components, since this is an example I will use it directly in the AppComponent, go to src/app/app.component.ts:

import {
  Component,
  ViewChildren,
  QueryList,
  ElementRef,
  AfterViewInit
} from '@angular/core';
import { TabTriggerComponent } from './shared/components/tab-trigger/tab-trigger.component';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.scss']
})
export class AppComponent implements AfterViewInit {
  @ViewChildren(TabTriggerComponent, { read: ElementRef })
  tabElements: QueryList<ElementRef>;
  tabs: ElementRef[];
  activated = 0;
  focused = 0;

  ngAfterViewInit() {
    this.tabs = this.tabElements.toArray();
    this.tabElements.first.nativeElement.firstChild.tabIndex = '0';
  }

  activatePanel(index: number) {
    this.tabs.forEach(tab => (tab.nativeElement.firstChild.tabIndex = -1));
    this.tabs[index].nativeElement.firstChild.tabIndex = index.toString();
    this.focused = index;
    this.activated = index;
  }

  focusPanel(index: number) {
    this.focused = index;
    this.tabs[this.focused].nativeElement.firstChild.focus();
  }

  handleKeyUp(event: KeyboardEvent) {
    switch (event.key) {
      case 'ArrowLeft':
        this.focusPanel(this.focused ? this.focused - 1 : this.tabs.length - 1);
        break;
      case 'ArrowRight':
        this.focusPanel((this.focused + 1) % this.tabs.length);
        break;
    }
  }

  handleKeyDown(event: KeyboardEvent) {
    switch (event.key) {
      case 'Home':
        event.preventDefault();
        this.focusPanel(0);
        break;
      case 'End':
        event.preventDefault();
        this.focusPanel(this.tabElements.length - 1);
        break;
    }
  }
}

Let walk through this component:

We're using @ViewChildren to get all the TabTriggerComponent instances.
Using the AfterViewInit life cycle, I get a clone of the component instances, and set tabindex=0 to the first one.
A method activatePanel, used when any of the triggers is clicked.
A method focusPanel, triggering the focus in the Button Element.
A method handleKeyUp and handleKeyDown. We separate them because Home and End keys have a default behavior that needs to be prevented.

Now, open the template in src/app/app.component.html:

<main>
  <div class="tabs">
    <div
      role="tablist"
      aria-label="options"
      (keyup)="handleKeyUp($event)"
      (keydown)="handleKeyDown($event)"
    >
      <app-tab-trigger
        triggerId="trigger-a"
        panelId="panel-a"
        [isActive]="activated === 0"
        (click)="activatePanel(0)"
      >
        Panel A
      </app-tab-trigger>
      <app-tab-trigger
        triggerId="trigger-b"
        panelId="panel-b"
        [isActive]="activated === 1"
        (click)="activatePanel(1)"
      >
        Panel B
      </app-tab-trigger>
      <app-tab-trigger
        triggerId="trigger-c"
        panelId="panel-c"
        [isActive]="activated === 2"
        (click)="activatePanel(2)"
      >
        Panel C
      </app-tab-trigger>
    </div>

    <app-tab-panel
      *ngIf="activated === 0"
      panelId="panel-a"
      triggerId="trigger-a"
    >
      <p>Panel A</p>
    </app-tab-panel>
    <app-tab-panel
      *ngIf="activated === 1"
      panelId="panel-b"
      triggerId="trigger-b"
    >
      <p>Panel B</p>
    </app-tab-panel>
    <app-tab-panel
      *ngIf="activated === 2"
      panelId="panel-c"
      triggerId="trigger-c"
    >
      <p>Panel C</p>
    </app-tab-panel>
  </div>
</main>

And now, the final styles to the AppComponent! Open src/app/app.component.scss:

.tabs {
  width: 20em;
}

[role='tablist'] {
  margin: 0 0 -0.1em;
  overflow: visible;
}

Conclusion

After a few quick steps, we were able to replicate the WAI-ARIA spec for Tabs, using a component oriented approach with Angular's help. I heavily based my implementation on the one found in the spec. My goal was primarily to show how easy it is to use Angular concepts to build such a feature. If you encounter any issues while trying to do this, drop a comment below.

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Making Seamless Page Transitions with the View Transitions API

Make Seamless Page Transitions using the View Transitions API Traditionally web applications have always had a less polished experience, both functionally and visually speaking, compared to native applications on mobile and other platforms. This has been improving over the years with the introduction of new web APIs and standards. One such new API that bridges that gap is the View Transitions API. What is the View Transitions API? The View Transitions API is a new browser feature that allows developers to more easily create animated transitions between pages and views, similar to how mobile apps have transitions when navigating between pages. Adding view transitions to your application can reduce the cognitive load on your users and make the experience feel less inconsistent. One great thing about view transitions is that they can be used by both SPAs (single-page applications) and MPAs (multi-page applications) alike! Using the View Transitions API for SPAs Let’s see how we can use view transitions ourselves. We will use examples adapted from demos created by the wonderful Jake Archibald and Bramus. There are some alterations to a few of the examples to make them work with the newest version of the View Transitions API, but otherwise, they’re mostly the same. The process of getting view transitions working for SPAs is as simple as calling document.startViewTransition right before starting navigation and replacing your page’s content immediately after that. You need to make this call in your router or in an event listener that triggers your page navigation. The following is an example of how you can hook into page navigation in a vanilla JavaScript application. This example uses the Navigation API if it’s available. As of the time of writing this article only Chromium-based browsers support the Navigation API, but there is a fallback to using a click listener on link elements so that this works with Firefox and Safari. ` If you’re using a framework, then there’s probably a better way to do this specific to that framework than by using this contrived example. For example, if you are implementing usage of this API with a Next application, you may opt for something like next-view-transitions. For this article, we’re going to focus on the way this is done in vanilla JavaScript so that the fundamentals of using the API are understood. Knowing how it’s implemented in vanilla JavaScript should give you enough understanding to implement this in the framework of your choice if there isn’t already a library that does it for you. Now we have a way to know when a navigation is being requested. Using the above utility function we can start the animation and replace our content as follows: ` getMyPageContentSomehow can be any function that returns HTML. How that is implemented will depend on your application and framework of choice. If you want to run these examples on your machine, the demo repository has instructions in its README. In essence, it’s as simple as hosting an HTTP server at the root of the project and visiting localhost. No fancy build system is required! By default, a fade is done that only lasts for a moment. The animation that happens can be configured using CSS with the ::view-transition-group pseudo-element on the element you want to animate, which in our case is the entire page, and we pass in root. ` Given that the animation properties are used, you have much control over what kind of animation to do. You can change the duration and the interpolation, add keyframes and gradients, and even add image masks. You can learn more about the animation properties in CSS on MDN. Using the View Transitions API for MPAs As mentioned, view transitions also work for MPAs with no client-side routing. Setting up view transitions for MPAs is much easier than for SPAs. All you have to do is include the CSS rule on all pages where you want the animations. ` Of course, like how it works with SPAs, you can customize the animations to your heart’s content using the view transition pseudo-elements. Conclusion I hope this article helped you understand the fundamentals of using the View Transitions API. Now that most browsers support it and it’s not too difficult to add it to existing applications, it is a great time to learn how to use it. You can view a full list of examples here (made by Jake Archibald and Bramus) if you want to see how advanced the animations can get. I like the Star Wars ones especially. The README explains how to get all the examples up and running (a total of 43!)....

Aug 2, 2024

4 mins

JavaScript

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

Understanding the Difference Between `:focus` and `:focus-visible` in CSS

Understanding the Difference Between :focus and :focus-visible in CSS I have learned my fair share about the importance of keyboard accessibility, so I know that visual indication of the focused element is very important. But the well-known :focus pseudo-class is not always the best fit for this job. That's where :focus-visible comes in. Let's look at the differences between these two pseudo-classes and explore the best practices for using them effectively. What is the :focus Pseudo-Class? The :focus pseudo-class is a CSS selector that applies styles to any element that receives focus, regardless of how that focus was triggered. This includes focus events from keyboard navigation, mouse clicks, and touch interactions. Example Usage of :focus ` In this example, the button will display a blue outline whenever it is focused, whether the user clicks on it with a mouse, taps it on a touchscreen, or navigates to it using the keyboard. What is the :focus-visible Pseudo-Class? The :focus-visible pseudo-class is more specialized. It only applies styles to an element when the browser determines that the focus should be visible. This typically occurs when the user navigates via the keyboard or assistive technologies rather than through mouse or touch input. Example Usage of :focus-visible ` Here, the button will only show a blue outline when focused through keyboard navigation or another input method that usually requires visible focus indicators. Key Differences Between :focus and :focus-visible :focus - Behavior: Applies to any element that receives focus, regardless of the input method. - Use Cases: Ensures that all interactions with the element are visually indicated, whether by mouse, keyboard, or touch. :focus-visible - Behavior: Applies styles only when the focus should be visible, such as using a keyboard or assistive technology. - Use Cases: Ideal for scenarios where you want to provide focus indicators only to keyboard and assistive technology users while avoiding unnecessary outlines for mouse and touch users, typically required by design. Accessibility Implications :focus - Pros: - Guarantees that all users can see when an element is focused, which is critical for accessibility. - Cons: - Can lead to a suboptimal experience for mouse users, as focus styles may appear unnecessarily during mouse interactions. :focus-visible - Pros: - Enhances user experience by showing focus indicators only when necessary, thus keeping the interface clean for mouse and touch users. - Tailors the experience for keyboard and assistive technology users, providing them with clear visual cues. - Cons: - Additional considerations may be required to ensure that focus indicators are not accidentally omitted, especially in older browsers that do not support :focus-visible. - There may be cases where you want to show focus indicators for all users, regardless of input method. Best Practices for Using :focus and :focus-visible To achieve the best accessibility and user experience, combining both :focus and :focus-visible in your CSS is often a good idea. Combining :focus and :focus-visible ` Here is a Stackblitz example of what such styling could look like for you to try out and play with. Additional Tips - Test with Keyboard and Assistive Technology: Ensure that your web application is navigable using a keyboard (Tab, Shift + Tab, etc.) and that focus indicators are visible for those who rely on them. It's never a bad idea to include accessibility testing in your e2e testing suite. - Provide Clear Focus Indicators: Make sure that focus indicators are prominent and easy to see. A subtle or hard-to-spot focus indicator can severely impact accessibility for users who rely on keyboard navigation. Conclusion The :focus-visible pseudo-class offers a more refined way to manage focus indicators, improving accessibility and user experience, particularly for keyboard and assistive technology users. By understanding the differences between :focus and :focus-visible, and applying best practices in your CSS, you can create more accessible and user-friendly web applications. Remember, accessibility should never be an afterthought. By thoughtfully applying focus styles, you ensure that all users, regardless of how they interact with your site, can easily navigate and interact....

Nov 8, 2024

3 mins

AccessibilityCSSPlaywright

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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The Implementation

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Tab Panel

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