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

In the last section, you refactored each component to use the 

 that has started to get polluted with logic is the 

 features several event listeners that bind each 

 method using arrow brackets to ensure the context (

connectedCallback() {
  for (let prop in this.$attr) {
    this.$input.setAttribute(prop, this.$attr[prop]);
  }
  this.$input.onblur = () => {
    this.onValidate(true);
  };
  this.$input.onchange = () => {
    this.onChange();
  };
  this.$input.onkeyup = () => {
    this.onChange();
  };
  this.onValidate(false);
}

 because the component template can be reliably queried in this lifecycle method. Listening for events is fairly common practice in web development, so perhaps the micro-library could provide a better interface for binding 

 methods to event listeners. Enter method decorators. In the example below, a method decorator named 

 name and optionally, a selector that could be passed to 

. This all happens behind the scenes now. 

 has direct access to the method it decorates, so we can pass the method to the second argument of 

 method the callback that is called when the 

  @Listen('blur', 'input')
  onValidate() {
    validate(this, true);
  }

Method decorators are composible. If the same callback applies to two different event listeners, you can stack the decorators on the method and expect both to work just fine.

@Listen('change', 'input')
@Listen('keyup', 'input')
onChange() {
  this.shadowRoot.querySelector('.message').innerHTML = '';
  this.$input.classList.remove('error');
  this.$input.removeAttribute('aria-invalid');
  this.internals.setFormValue(this.value, this.value);
}

If we were to implement the method decorator pattern, this would virtually eliminate the need to bind event listeners in 

connectedCallback() {
  for (let prop in this.$attr) {
    this.$input.setAttribute(prop, this.$attr[prop]);
  }
  validate(this, false);
}

Method decorators are arguably more statically analyzable as well, given that engineers have the option of calling methods on the element (

 for event listening. A method decorator standardizes the practice of coding for events. Developers can forget to remove event listeners when an element is removed from DOM. To be safe, you have to call 

 callback to remove the event listener. That is another potential flaw method decorators can remedy. When coding the 

 decorator you'll observe that we still bind event listeners in much the same way, along with the 

, but we can also automate removal of event listeners in the 

, all without interfering with an engineer's code.

Method decorators, unlike class decorators, have access to the 

 with a decorator you only had access to the 

, but with method decorators you can expect the context (

, but for reliability the safest place to modify a 

For the rest of this section, you'll code a method decorator named 

. The decorator needs to bind the method it modifies to the second argument of 

. Method decorators are just functions, so you'll pass the event name as the first argument and the element that 

 should be called on as the second argument. This second argument will be optional, as the method decorator can by default call 

 if the end-user doesn't specify a second argument.

touch packages/common/src/event/listen.ts

 package for use in other packages of the monorepo. First mock the 

, being sure to make it exportable. The first argument is named 

export function Listen(eventName: string, selector?: string) {}

 returns a factory function that can be type defined. Make a new type definition using the 

. This type definition will describe the function returned by any method decorator. This 

 that describes the configuration of the property on class Object. What's important to remember about the 

 that equals the actual method being decorated.

 and declare all three arguments. The boilerplate for the 

type MethodDecoratorFactoryFunction = (
  target: any,
  key: string | number,
  descriptor: PropertyDescriptor
) => void;

export function Listen(
  eventName: string,
  selector?: string
): MethodDecoratorFactoryFunction {
  return function decorator(
    target: any,
    key: string | number,
    descriptor: PropertyDescriptor
  ) {};
}

In the decorator function, we'll need a few things to achieve the end goal.

That's a lot to unpack. It's not by virtue of being a method decorator that 

. The problem we have to solve is that much more sophisticated. Let's take it step by step.

 destructuring. Assign both to noop functions because we don't want to override the user's declared 

const { connectedCallback = () => {}, disconnectedCallback = () => {} } =
  target;

We need a reliable way to access the method over time. In one 

, we'll need to pass the method that is decorated to 

. One way to ensure the method never changes is to assign the method to a 

, which is guaranteed to be unique. Make a new 

). This is mainly so we can access the method like 

---
title: Method Decorator
description: You'll code a method decorator named Listen that binds event listeners to class methods.
isPublicLesson: true
---

## Method Decorator

In the last section, you refactored each component to use the `Component` class decorator. That cleaned up the `constructor` of each component `class` fairly nicely. Another method on the `class` that has started to get polluted with logic is the `connectedCallback`. In `TextInputComponent`, the `connectedCallback` features several event listeners that bind each `function` callback to a `class` method using arrow brackets to ensure the context (`this`) is the `class` and not `this.$input`.

```typescript
connectedCallback() {
  for (let prop in this.$attr) {
    this.$input.setAttribute(prop, this.$attr[prop]);
  }
  this.$input.onblur = () => {
    this.onValidate(true);
  };
  this.$input.onchange = () => {
    this.onChange();
  };
  this.$input.onkeyup = () => {
    this.onChange();
  };
  this.onValidate(false);
}
```

Binding event listeners to `function` callbacks is fairly common practice in `connectedCallback` because the component template can be reliably queried in this lifecycle method. Listening for events is fairly common practice in web development, so perhaps the micro-library could provide a better interface for binding `class` methods to event listeners. Enter method decorators. In the example below, a method decorator named `Listen` augments the behavior of `onValidate`. `Listen` is a `function` that takes two arguments: the `Event` name and optionally, a selector that could be passed to `querySelector` to bind the event to an element using `addEventListener`. This all happens behind the scenes now. `Listen` has direct access to the method it decorates, so we can pass the method to the second argument of `addEventListener` making the `class` method the callback that is called when the `Event` happens.

```typescript
  @Listen('blur', 'input')
  onValidate() {
    validate(this, true);
  }
```

Method decorators are composible. If the same callback applies to two different event listeners, you can stack the decorators on the method and expect both to work just fine.

```typescript
@Listen('change', 'input')
@Listen('keyup', 'input')
onChange() {
  this.shadowRoot.querySelector('.message').innerHTML = '';
  this.$input.classList.remove('error');
  this.$input.removeAttribute('aria-invalid');
  this.internals.setFormValue(this.value, this.value);
}
```

If we were to implement the method decorator pattern, this would virtually eliminate the need to bind event listeners in `connectedCallback`, freeing up the method for other logic.

```typescript
connectedCallback() {
  for (let prop in this.$attr) {
    this.$input.setAttribute(prop, this.$attr[prop]);
  }
  validate(this, false);
}
```

Method decorators are arguably more statically analyzable as well, given that engineers have the option of calling methods on the element (`onchange`) or using `addEventListener('change')` for event listening. A method decorator standardizes the practice of coding for events. Developers can forget to remove event listeners when an element is removed from DOM. To be safe, you have to call `removeEventListener` on the `disconnectedCallback`, passing in the `function` callback to remove the event listener. That is another potential flaw method decorators can remedy. When coding the `Listen` decorator you'll observe that we still bind event listeners in much the same way, along with the `connectedCallback`, but we can also automate removal of event listeners in the `disconnectedCallback`, all without interfering with an engineer's code.

Method decorators, unlike class decorators, have access to the `class` instance. When modifying the `class` with a decorator you only had access to the `prototype`, but with method decorators you can expect the context (`this`) to point to the instance of the `class`. Method decorators can deconstruct the `class` and do things with the `prototype`, but for reliability the safest place to modify a `prototype` is the class decorator.

For the rest of this section, you'll code a method decorator named `Listen`, then apply that decorator to `TextInputComponent`. The decorator needs to bind the method it modifies to the second argument of `addEventListener`. Method decorators are just functions, so you'll pass the event name as the first argument and the element that `addEventListener` should be called on as the second argument. This second argument will be optional, as the method decorator can by default call `this.addEventListener` if the end-user doesn't specify a second argument.

To get started, make a new directory in `packages/common/src` named `event`.

```bash
mkdir packages/common/src/event
```

Create a new file named `listen.ts` in `packages/common/src/event`.

```bash
touch packages/common/src/event/listen.ts
```

## Define the Listen decorator

In this file, you'll develop the `Listen` decorator, then export the `function` from the `@in/common` package for use in other packages of the monorepo. First mock the `function`, being sure to make it exportable. The first argument is named `eventName`, type defined as a `string`. This argument will be passed to `addEventListener`. The second argument named `selector` is optional, denoted with `?` in TypeScript and also typed as `string`. This `string` will be passed to `querySelector`.

```typescript
export function Listen(eventName: string, selector?: string) {}
```

`Listen` returns a factory function that can be type defined. Make a new type definition using the `type` keyword and name it `MethodDecoratorFactoryFunction`. This type definition will describe the function returned by any method decorator. This `function` has three arguments: `target` is the instance of the `class` the method is found, `key` is the name of the method as a `string`, and descriptor is a `PropertyDescriptor`, which gets its type definition from `lib.dom.d.ts`. `PropertyDescriptor` is an `Object` that describes the configuration of the property on class Object. What's important to remember about the `PropertyDescriptor` is that it stores a property named `value` that equals the actual method being decorated.

Apply the `MethodDecoratorFactoryFunction type` to the returns type of the `Listen function`, then return a `function` named `decorator` and declare all three arguments. The boilerplate for the `Listen` decorator is below.

```typescript
type MethodDecoratorFactoryFunction = (
  target: any,
  key: string | number,
  descriptor: PropertyDescriptor
) => void;

export function Listen(
  eventName: string,
  selector?: string
): MethodDecoratorFactoryFunction {
  return function decorator(
    target: any,
    key: string | number,
    descriptor: PropertyDescriptor
  ) {};
}
```

In the decorator function, we'll need a few things to achieve the end goal.

-   `function` that calls `addEventListener`
-   `function` that calls `removeEventListener`
-   Store the method set as the `function` callback on `addEventListener` so we can call `removeEventListener` with the same method
-   Hook into `connectedCallback` and `disconnectedCallback` to call both `function` that add and remove the listeners
-   Call `addEventListener` and `removeEventListener` on `this` unless a `selector` is specified, then query for an element using the selector and attach `addEventListener` and `removeEventListener`