Acknowledgements

The beginning of your journey with Web Components.

Foreword

A brief introduction to the set of specifications called Web Components. We'll introduce you to concepts such as Shadow DOM, HTML templates, Custom Elements v1 and uncover typical use cases for developing Web Components.

Introduction to Web Components

We'll introduce you to the mockups in Figma, the development environment used throughout the book, and other conventions used in this book.

Conventions Used In The Book

A guide for installing various technologies needed prior to coding the exercises in this book.

Setting Up The Development Environment

We'll look at what you'll learn throughout Fullstack Web Components.

Module 1 Summary

Introduction

In Part 1, you'll code a form using several Web Components specifications.

Specification

Part One

By developing the CardComponent, you'll get hands on experience with autonomous custom elements.

Autonomous custom elements

Before you can develop the CardComponent, you'll need to scaffold the component in Storybook.

Template Slots

Shadow DOM provides encapsulation for styling and template. You'll style CardComponent with CSS in the context of the autonomous custom element's Shadow DOM.

Styling CardComponent

Write integration and snapshot tests for CardComponent using Cypress and Storybook Storyshots.

Testing the card

You built an autonomous custom element with Shadow DOM, HTML templates, and ES Modules. Let's reflect on that.

Chapter One Summary

Getting to Know Web Components

Form-associated custom elements allow custom elements to participate in HTML forms. From validation to submission, you'll code a text input end-to-end.

Form-associated custom elements

Scaffold a form-associated custom element named TextInputComponent in Storybook.

TextInputComponent

You'll learn what distinguises a form-associated custom element from an autonomous custom element, the formAssociated property and ElementInternals interface.

Form Associated and ElementInternals

Form-associated custom elements don't come with a pattern that validates an entire form, so you'll implement a pattern that allows form validation.

Handling Validation

Using observedAttributes and attributeChangedCallback to listen and react to changes in custom element attributes.

Listening for attribute changes

You'll style the various interaction states of the TextInputComponent form-associated custom element.

User feedback

We've created a problem by encapsulating the HTMLInputElement by Shadow DOM. The HTMLInputElement API cann't be accessed by the outside world. In this section, you'll fix that by implementing getters and setters that emulate the HTMLInputElement on TextInputComponent.

Emulating HTMLInputElement

You'll update the Story and provide the missing APIs to TextInputComponent that allow the component to fully interact with a HTML form.

Making a form

Reviewing the work completed on the form-associated custom element TextInputComponent.

Chapter Two Summary

You'll code ButtonComponent, a customized built-in element that inherits accessibility characteristics from HTMLButtonElement.

Customized built-in elements

Scaffold the customized built-in element ButtonComponent with Storybook.

Scaffolding ButtonComponent

Customized built-ins can't benefit from the encapsulation provided by Shadow DOM, so you'll have to find another way to style ButtonComponent.

Styling ButtonComponent

Revist the HTML form by making the user experience more accessible.

Making the form accessible

How customized built-in elements can make custom elements more accessible.

Chapter Three Summary

You'll learn best practices for developing a UI Library with Web Components by coding a micro-library, developing two custom elements with the micro-library, and figuring out how to package the UI library for distribution.

UI Library

Part Two

You'll abstract common patterns intro reusable code in a micro-library powered by TypeScript Decorators.

Micro-library

How to code an interface for Web Components with TypeScript decorators that enables declaration of the selector, styles, and template.

Class Decorator

You'll code a method decorator named Listen that binds event listeners to class methods.

Method Decorator

In this chapter you learned how to code a micro-library with TypeScript decorators that streamlines Web Component development.

Chapter Four Summary

You'll investigate multiple methods for components to communicate by coding an editable table.

Component Communication

How to use mock data in Storybook to code Web Components.

Mocking Table Data in Storybook

You'll learn about three methods for custom elements to communicate, attribute drilling, CustomEvent, and BroadcastChannel.

Coding Compound Components

You'll learn about how to create a separation of concerns between the many custom elements that comprise the editable table.

Making the Table Editable

You learned about how to create a separation of concerns between various custom elements in the same user experience flow.

Summary

Compound Custom Elements

You'll learn how to code a common UX pattern (dialogs) using HTML templates and custom elements.

HTML Templates

You'll mock the DialogComponent in Storybook.

Mocking the Dialog in Storybook

You'll make a configurable dialog with custom elements.

DialogComponent

You'll scaffold two custom elements that leverage DialogComponent to display modals and tooltips.

Modal and Tooltip

You'll fix an issue faced in the last section by learning how to query for elements across Shadow boundaries.

Querying DOM Across Shadow Boundaries

You'll control the ordering and event cycle of dialogs with a custom class named DialogStack.

DialogStack

Summarizing the work completed in DialogComponent, ModalComponent, TooltipComponent, and DialogStack.

Chapter Six Summary

Powering Dialogs with HTML Templates

You'll learn best practices for organizing and distributing Web Component UI libraries.

UI Libraries

You'll learn brest practices for distributing Web Components by formatting the code with named exports, configuring the build with Rollup, providing a standard package format, and writing a custom Node.js script that enables you to publish packages.

Distribution

Custom Elements Manifest provides a wealth of information about each component. After generating a manifest, it will provide documentation for each component in Storybook.

Documentation

You'll learn how to setup continuous integration for the UI library with Github Actions.

Continuous Integration

Let's reflect on the best practices you learned for distributing UI libraries filled with Web Components.

Chapter Seven Summary

Distributing Custom Element Libraries

You'll integrate the UI library with a single-page application and code the end-to-end user experience with custom elements.

Application

Part Three

You'll provide a separation of concerns with custom elements in a single page application.

Application Development with Custom Elements

You'll scaffold the landing page with an autonomous custom element named MainView.

Landing Page

You'll code a global header with autonomous custom elements named AppHeader.

Header

You'll code another autonomous custom element that handles cookie authorization named CookieFooter.

CookieFooter

You'll lazyload an image with customized built-ins.

Background

You developed the landing page of the application, learning how to architect a separation of concerns between the UI components.

Chapter Eight Summary

To handle multiple views in the single page application, you'll need to implement a router that can navigate between each view.

Routing Custom Elements in a SPA

You'll code the Router class that handles the creation and removal of views in the application.

Routing

You'll code the necessary components and services required in the login view.

Login View

Integrate TableCardComponent into a third view of the single page application, the dashboard.

Dashboard View

You coded a single page web application with custom elements and a custom router.

Chapter Nine Summary

You'll server-side render the views of the application with Declarative Shadow DOM and @lit-labs/ssr

Server-Side Rendering Custom Elements

You'll declare a server-side renderable Declarative Shadow DOM HTML template for each component.

Declarative Shadow DOM Templates

To get custom elements to work in Node.js, you'll need to polyfill DOM APIs. Luckily, @lit-labs/ssr provides a tool that enables just that.

Shim

You'll develop Express middleware that server-side renders Declarative Shadow DOM HTML Templates with @lit-labs/ssr.

Express Middleware

You rendered custom elements server-side using Declarative Shadow DOM and @lit-labs/ssr.

Chapter Ten Summary

Server-side Rendering with Declarative Shadow DOM

The conclusion of the book Fullstack Custom Elements.

Conclusion

Fullstack Web Components

Enter your name and email address below, then click the **"Send my free chapter"** button to get started

There are several books about Web Components, but none go into how to integrate Web Components in a typical enterprise web development workflow. This book is designed to help you learn Web Components and integrate it into your work.

In this book, we cover the basics of Web Components, how to code complex user interfaces with custom elements in Storybook, how to test and maintain UI libraries built with custom elements, and how to build web applications entirely with Web Components and browser specifications. It comes with complete code examples. We walk through the entire process step-by-step.

It's taught by Stephen Belovarich, a software engineer and web developer. Stephen has provided what he's learned about UI libraries and web applications while working at Ubiquiti Networks, Norton, Nike, NBC Universal, and Workday, that can benefit other developers, students, and anyone making a website.

The Complete Guide to Building UI Libraries with Web Components

In this book, we will learn Web Components through the lens of a JavaScript developer.

The basics of working with and manipulating Web Components

The best practices for maintaining a UI library made of custom elements

How to create a micro-library for Web Components with TypeScript Decorators

What problems Web Components can solve in everyday development

How to build web applications entirely from Web Components and JavaScript

Whether it's a login view, checkout in an e-commerce app, or a table where every cell is editable, there's no shortage of form controls in modern applications. Autonomous custom elements have some problems when working in the context of HTML forms. When a form control is encapsulated by Shadow DOM, like in the case of this input, the form control cannot participate in the parent 

 should report validity and it's value to a parent 

, however, the Shadow DOM boundary blocks communication between the form and input.

When a form control is encapsulated by Shadow DOM, the element:

When form inputs are not properly configured, accessibility issues can also arise because screen readers expect form controls to have specific relationships with elements that label them. Shadow DOM can break the connection between a label and form control.

Form-associated custom elements solve these problems by introducing the 

 interface allows the custom element to participate in a form like any typical form control. Native form controls like 

 already employ similar methods found on the 

 interface that allow them to register with the 

 and participate in the form, but if the form control is contained in Shadow DOM, those methods are inaccessible to the form.

 is provided to an autonomous custom element by calling 

. It's typical to set another property on the 

 so you can reference it later. When an autonomous custom element is configured in such a way, it becomes a form-associated custom element.

export class TextInputComponent extends HTMLElement {
  static formAssociated = true;
  private internals: IElementInternals;
   constructor() {
    super();
    attachShadow(this);
    this.internals = this.attachInternals();
  }

 provides a bunch of utility methods on the custom element 

, so the custom element can retain all the accessibility characteristics expected from a form control. 

In this chapter, you'll code a form control used throughout the application: 

. This element displays editable text input and a list of validation messages to a user.

---
title: Form-associated custom elements
description: Form-associated custom elements allow custom elements to participate in HTML forms. From validation to submission, you'll code a text input end-to-end.
role: "INTRODUCTION"
isPublicLesson: true
---

# Chapter Two

## Introduction

Whether it's a login view, checkout in an e-commerce app, or a table where every cell is editable, there's no shortage of form controls in modern applications. Autonomous custom elements have some problems when working in the context of HTML forms. When a form control is encapsulated by Shadow DOM, like in the case of this input, the form control cannot participate in the parent `HTMLFormElement`. By default, the `HTMLInputElement` should report validity and it's value to a parent `HTMLFormElement`, however, the Shadow DOM boundary blocks communication between the form and input.

![](https://d2uusema5elisf.cloudfront.net/courses/fullstack-web-components/module_04/lesson_04.01/public/assets/TextInput.no-required.png)

When a form control is encapsulated by Shadow DOM, the element:

-   Will not be listed under the parent `HTMLFormElement` node list
-   Can't be validated alongside other form controls properly
-   Won't be included in form submission

When form inputs are not properly configured, accessibility issues can also arise because screen readers expect form controls to have specific relationships with elements that label them. Shadow DOM can break the connection between a label and form control.

Form-associated custom elements solve these problems by introducing the [`ElementInternals`](https://developer.mozilla.org/en-US/docs/Web/API/ElementInternals) interface on the custom element. The `ElementInternals` interface allows the custom element to participate in a form like any typical form control. Native form controls like `HTMLInputElement` and `HTMLTextAreaElement` already employ similar methods found on the `ElementInternals` interface that allow them to register with the `HTMLFormElement` and participate in the form, but if the form control is contained in Shadow DOM, those methods are inaccessible to the form.

When the [`formAssociated`](https://html.spec.whatwg.org/multipage/custom-elements.html#custom-elements-face-example) property is set to `true` on the custom element `class`, `ElementInternals` is provided to an autonomous custom element by calling `attachInternals()`. It's typical to set another property on the `class` to an instance of `ElementInternals` so you can reference it later. When an autonomous custom element is configured in such a way, it becomes a form-associated custom element.

```typescript
export class TextInputComponent extends HTMLElement {
  static formAssociated = true;
  private internals: IElementInternals;
   constructor() {
    super();
    attachShadow(this);
    this.internals = this.attachInternals();
  }
```

`ElementInternals` provides a bunch of utility methods on the custom element `prototype` used to:

-   Validate the form control
-   Assign labels for screen readers
-   Communicate state used during form submission
-   handle accessibility behaviors

The `ElementInternals` interface includes the entire [Accessibility Object Model](https://wicg.github.io/aom/spec/), so the custom element can retain all the accessibility characteristics expected from a form control. [A full reference of `ElementInternals` interface is provided on MDN.](https://developer.mozilla.org/en-US/docs/Web/API/ElementInternals).