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

Now that you have a test bed where validation state can be verified during development, it's a good time to handle user feedback. According to the mockups in Figma, whenever there is an error associated with a form control:

 whenever the user blurs the form control. Perhaps this is also a good place to handle user feedback. However, since 

 is a reusable function that could be used in other components, it means any elements referenced here must be found in all of those custom elements. In 

 template, two elements are used to provide user feedback: the input (

  const messageElem = elem.shadowRoot.querySelector(".message");

To prevent errors when a form control doesn't include this element, be sure to check if 

 to an empty string. This is necessary because existing messages could have accumulated in the element, and in the case of the form control being valid, we need a way to clear them.

  if (messageElem) {
    messageElem.innerHTML = "";
  }

 is truthy, include some logic to show the error state when the second argument 

. Again, check for the elements before interacting with them. Add a class to the input named 

 and create a new div, set its content to whatever is in 

      if (showError) {
        if (elem.$input) {
          elem.$input.classList.add("error");
        }
        if (messageElem) {
          const div = document.createElement("div");
          div.innerHTML = validator.message;
          messageElem.appendChild(div);
        }
      }

When the form control is valid, remove the 

 class from the input element and reset the content of 

 to an empty string. This has the effect of clearing the error state.

  if (!activeValidators.length) {
    elem.setValidity({});
    if (elem.$input) {
      elem.$input.classList.remove("error");
    }
    if (messageElem) {
      messageElem.innerHTML = "";
    }
  }

Test out the changes in Storybook. Click on the input and immediately blur, either by clicking outside the input or pressing Tab on the keyboard. You should notice the message "

" below the input. Focus the input, and this time enter a value, and then blur the input, causing the message to disappear. Repeat this process, inspecting the DOM in Dev Tools to ensure that the 

 class is added and removed from DOM at the appropriate times.

Pretty soon, you'll style the input with CSS like the mockup in Figma, and the look and feel will get a substantial improvement. Before you engage in styling, there's one more state you'll need to handle in 

Form controls can be disabled by setting the 

 attribute on the element, or when the element is a descendant of a 

, it should inherit its disabled state. Form-associated custom elements include a lifecycle hook for this specific use-case called 

 is a child to a disabled fieldset in DOM, this callback will be activated. Whenever 

 is called, the first argument contains the disabled state. Pass this state to the 

  formDisabledCallback(disabled) {
    this.disabled = disabled;
  }

TypeScript should throw an error because you haven't yet established a setter for the 

 from before, syncing the child input element with the current value of the 

  set disabled(value: boolean | string) {
    if (value === "true" || value === true) {
      this.$input.setAttribute("disabled", "true");
    }
    if (value === "false" || value == false) {
      this.$input.removeAttribute("disabled");
    }
  }

Declare a getter that returns the disabled state from the 

  get disabled() {
    return this.$input.disabled;
  }

      case "disabled":
        this.disabled = next;
        break;

 a disabled state. When a developer sets the 

 disabled state. Developers can read the disabled state with the 

 getter. Whenever a parent fieldset is disabled, the 

 to set the disabled state of the component via the setter.

---
title: User feedback
description: You'll style the various interaction states of the TextInputComponent form-associated custom element.
isPublicLesson: true
---

## User feedback

Now that you have a test bed where validation state can be verified during development, it's a good time to handle user feedback. According to the mockups in Figma, whenever there is an error associated with a form control:

-   The input border should change color to a shade of red
-   Messages that instruct the user how to validate the form control are displayed below the input

So far in the `validate function`, you've called `setValidity` whenever the user blurs the form control. Perhaps this is also a good place to handle user feedback. However, since `validate` is a reusable function that could be used in other components, it means any elements referenced here must be found in all of those custom elements. In `TextInputComponent` template, two elements are used to provide user feedback: the input (`elem.$input`) and a div with the class `message`.

In `validator.ts`, declare a new `const` named `messageElem`. Use `querySelector` to target the div with the class `message` in the `ShadowRoot` of the element.

```javascript { actualFilename=./protected/src/validator.ts endLine=15 startLine=15 statedFilename=validator.ts url=https&#x3A;//gitlab.com/fullstackio/books/fullstack-web-components/module_04/lesson_04.06/protected/src/validator.ts#L15 }
  const messageElem = elem.shadowRoot.querySelector(".message");
```

To prevent errors when a form control doesn't include this element, be sure to check if `messageElement` is truthy. Whenever `validate` is called, empty the `messageElement` of content by setting the `innerHTML` to an empty string. This is necessary because existing messages could have accumulated in the element, and in the case of the form control being valid, we need a way to clear them.

```javascript { actualFilename=./protected/src/validator.ts endLine=19 startLine=17 statedFilename=validator.ts url=https&#x3A;//gitlab.com/fullstackio/books/fullstack-web-components/module_04/lesson_04.06/protected/src/validator.ts#L17 }
  if (messageElem) {
    messageElem.innerHTML = "";
  }
```

In the `forEach`, whenever `validator.condition(elem)` is truthy, include some logic to show the error state when the second argument `showError` is `true`. Again, check for the elements before interacting with them. Add a class to the input named `error` and create a new div, set its content to whatever is in `validator.message`, and call `appendChild` on the `messageElem` to append the message.

```javascript { actualFilename=./protected/src/validator.ts endLine=33 startLine=24 statedFilename=validator.ts url=https&#x3A;//gitlab.com/fullstackio/books/fullstack-web-components/module_04/lesson_04.06/protected/src/validator.ts#L24 }
      if (showError) {
        if (elem.$input) {
          elem.$input.classList.add("error");
        }
        if (messageElem) {
          const div = document.createElement("div");
          div.innerHTML = validator.message;
          messageElem.appendChild(div);
        }
      }
```

When the form control is valid, remove the `error` class from the input element and reset the content of `messageElem` by setting the `innerHTML` to an empty string. This has the effect of clearing the error state.

```javascript { actualFilename=./protected/src/validator.ts endLine=46 startLine=38 statedFilename=validator.ts url=https&#x3A;//gitlab.com/fullstackio/books/fullstack-web-components/module_04/lesson_04.06/protected/src/validator.ts#L38 }
  if (!activeValidators.length) {
    elem.setValidity({});
    if (elem.$input) {
      elem.$input.classList.remove("error");
    }
    if (messageElem) {
      messageElem.innerHTML = "";
    }
  }
```

Test out the changes in Storybook. Click on the input and immediately blur, either by clicking outside the input or pressing Tab on the keyboard. You should notice the message "**Error: Required**" below the input. Focus the input, and this time enter a value, and then blur the input, causing the message to disappear. Repeat this process, inspecting the DOM in Dev Tools to ensure that the `error` class is added and removed from DOM at the appropriate times.

Pretty soon, you'll style the input with CSS like the mockup in Figma, and the look and feel will get a substantial improvement. Before you engage in styling, there's one more state you'll need to handle in `TextInputComponent` whenever the input is disabled.

## Handling Disabled State

Form controls can be disabled by setting the `disabled` attribute on the element, or when the element is a descendant of a `<fieldset>`, it should inherit its disabled state. Form-associated custom elements include a lifecycle hook for this specific use-case called `formDisabledCallback`. Whenever `TextInputComponent` is a child to a disabled fieldset in DOM, this callback will be activated. Whenever `formDisabledCallback` is called, the first argument contains the disabled state. Pass this state to the `TextInputComponent`.

```javascript { actualFilename=./protected/src/TextInput.disabled.ts endLine=64 startLine=62 statedFilename=TextInput.ts url=https&#x3A;//gitlab.com/fullstackio/books/fullstack-web-components/module_04/lesson_04.06/protected/src/TextInput.disabled.ts#L62 }
  formDisabledCallback(disabled) {
    this.disabled = disabled;
  }
```

TypeScript should throw an error because you haven't yet established a setter for the `TextInputComponent` called `disabled`. This setter looks a lot like `required` from before, syncing the child input element with the current value of the `disabled` attribute on the instance of `TextInputComponent`.

```javascript { actualFilename=./protected/src/TextInput.disabled.ts endLine=157 startLine=150 statedFilename=TextInput.ts url=https&#x3A;//gitlab.com/fullstackio/books/fullstack-web-components/module_04/lesson_04.06/protected/src/TextInput.disabled.ts#L150 }
  set disabled(value: boolean | string) {
    if (value === "true" || value === true) {
      this.$input.setAttribute("disabled", "true");
    }
    if (value === "false" || value == false) {
      this.$input.removeAttribute("disabled");
    }
  }
```

Declare a getter that returns the disabled state from the `HTMLInputElement`.

```javascript { actualFilename=./protected/src/TextInput.disabled.ts endLine=145 startLine=143 statedFilename=TextInput.ts url=https&#x3A;//gitlab.com/fullstackio/books/fullstack-web-components/module_04/lesson_04.06/protected/src/TextInput.disabled.ts#L143 }
  get disabled() {
    return this.$input.disabled;
  }
```

Add the `disabled` attribute to the `observedAttributes Array`, and then include a `case` in the `switch` statement found in `attributeChangedCallback` that calls the `disabled` setter whenever the `disabled` attribute changes on `TextInputComponent`, making sure to also add the `disabled` to the `Array` returned in `observedAttributes`.

```javascript { actualFilename=./protected/src/TextInput.lifecycle.ts endLine=108 startLine=106 statedFilename=TextInput.ts url=https&#x3A;//gitlab.com/fullstackio/books/fullstack-web-components/module_04/lesson_04.06/protected/src/TextInput.lifecycle.ts#L106 }
      case "disabled":
        this.disabled = next;
        break;
```