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

There are many reasons why you would want to server-side render user interfaces. Server-side rendering UI may increase performance for the end-user because all the content for a HTML document is pre-rendered, reducing the time to paint each element in the browser window. UI components rendered server-side may already be "hydrated" with content. By offloading processing of UI components to a server, the overall time it takes to render HTML can be more predictable. Client-side rendering can be less predictable because different browsers have varied performance.

Server-side rendering promotes SEO compliance, making server-side renderable pages more compatible with search engine crawlers and social media. UI components rendered with a single-page application framework are less compatible with SEO because nothing is rendered in a timely fashion for a web crawler to statically analyze a HTML document. By offloading network requests to the server and hydrating UI components server-side with content, you can improve the security of an application by removing the possibility of exposing sensitive customer data.

For awhile, it was seemingly impossible to server-side render custom elements. Shadow DOM is imperative; you code statements that tell the browser to instantiate a new Shadow Root. This Shadow Root is what provides the ability for custom elements to take advantage of CSS scoping, DOM encapsulation, and composability. While the Shadow DOM specification is powerful, due to its imperative nature, Shadow DOM isn't immediately server-side renderable. Browser specifications aren't natively available in server environments like Node.js. Node.js is built on the V8 JavaScript engine that originated in the Chrome browser, but Node.js lacks browser-specific specifications like the Document Object Model (DOM). If you were going to try to instantiate the 

 in a Node.js environment, there would be an error because 

 doesn't exist in the context of Node.js, for instance.

The lack of the DOM in Node.js presents an interesting problem when server-side rendering custom elements. All the necessary browser specifications would need to be "shimmed" or "polyfilled" before the custom element 

 could instantiate, then custom logic on the server would need to parse and output a server-side generated template. An npm package that did just that is 

, a package currently in maintenance mode, which was created by Github user 

 and brought support for Custom Elements v1 to Node.js. You could use this package to server-side render custom elements built with 

, or with some configuration, custom elements coded directly with browser specifications. This tool generated templates server-side that enabled sites built with custom elements to be SEO friendly and highly performant. 

 worked for static-site generation, but it lacked the ability to "hydrate" components. It became apparent to the web development community a specification that enabled server-side rendering was needed. Enter Declarative Shadow DOM.

Declarative Shadow DOM is a browser specification that enables Shadow Root to be declaratively instantiated in HTML. Looking at the 

 component you developed in the last chapter, let's see how Declarative Shadow DOM differs. Instead of imperatively declaring a Shadow Root, you can declare the Shadow Root directly on a HTML template using the 

 HTML attribute. In the example below that abbreviates the necessary styling and HTML template, 

 tag name is included in a template. Using Declarative Shadow DOM, the direct child of the 

 is a HTML template. The HTML template includes a Shadow Root with the HTML attribute 

 that would have otherwise been imperatively defined via a call to 

. The template includes the CSS styling and HTML for the component.

<app-header>
  <template shadowroot="open">
    <style>
      :host {
        display: flex;
        justify-content: space-between;
        align-items: center;
        height: 100px;
        padding-left: var(--margin-lg);
        padding-right: var(--margin-lg);
        border-bottom: var(--border-default);
      }
    </style>
    <button is="in-button" class="in-button icon logo"></button>
    <a href="/login" class="login-link" hidden>Login</a>
  </template>
</app-header>

In the below example, you can compare the Declarative Shadow DOM example above to the imperative style of declaring a Shadow Root you've used to define the template for each component developed in this book.

export class AppHeader extends HTMLElement {
  constructor() {
    super();
    const shadowRoot: ShadowRoot = this.attachShadow({ mode: "open" });
    const template = document.createElement("template");
    template.innerHTML = html`
      <style>
        :host {
          display: flex;
          justify-content: space-between;
          align-items: center;
          height: 100px;
          padding-left: var(--margin-lg);
          padding-right: var(--margin-lg);
          border-bottom: var(--border-default);
        }
      </style>
      <button is="in-button" class="in-button icon logo"></button>
      <a href="/login" class="login-link" hidden>Login</a>
    `;
    shadowRoot.appendChild(template.content.cloneNode(true));
  }
}

Declarative Shadow DOM enables server-side rendering because a template is expressed as a 

. Strings can be manipulated in any JavaScript environment. In the browser, HTML is parsed by the user agent which isn't present in the Node.js environment. If you attempted to use methods that create HTML like 

 on the server, that method would fail because it doesn't exist. By expressing the template as a 

, you can pass the template in the HTTP response from the server to the client: a browser that can parse the HTML template as DOM.

Once the browser receives a HTML response with elements that use Declarative Shadow DOM, the user agent parses the HTML template with the 

 attribute much like it would when calling 

. Components that have registered their ES2015 

 and rendered with Declarative Shadow DOM don't have to call 

. This presents a problem for components that imperatively declare their Shadow Root, and components that need to "hydrate" their template during instantiation. If a component imperatively calls 

 that also has its template defined declaratively, the component will render duplicates of the same template in the browser window.

To prevent this phenomenon, you can check if a Declarative Shadow Root exists prior to imperatively declaring a template for each component. This is possible because any custom element using Declarative Shadow DOM is already upgraded and will already have attached the Shadow Root prior to the 

export class AppHeader extends HTMLElement {
  constructor() {
    super();
    if (!this.shadowRoot) {
      const shadowRoot: ShadowRoot = this.attachShadow({ mode: "open" });
      const template = document.createElement("template");
      ...
    }
  }
}

When developing custom elements that can be rendered with Declarative Shadow DOM, it's important to separate the logic for template instantiation and component hydration. This allows for easier maintenance of custom elements and makes their instantiation more predictable.

---
title: Server-Side Rendering Custom Elements
description: You'll server-side render the views of the application with Declarative Shadow DOM and @lit-labs/ssr
role: "INTRODUCTION"
isPublicLesson: true
---

# Chapter Ten

## Server-Side Rendering Custom Elements

There are many reasons why you would want to server-side render user interfaces. Server-side rendering UI may increase performance for the end-user because all the content for a HTML document is pre-rendered, reducing the time to paint each element in the browser window. UI components rendered server-side may already be "hydrated" with content. By offloading processing of UI components to a server, the overall time it takes to render HTML can be more predictable. Client-side rendering can be less predictable because different browsers have varied performance.

Server-side rendering promotes SEO compliance, making server-side renderable pages more compatible with search engine crawlers and social media. UI components rendered with a single-page application framework are less compatible with SEO because nothing is rendered in a timely fashion for a web crawler to statically analyze a HTML document. By offloading network requests to the server and hydrating UI components server-side with content, you can improve the security of an application by removing the possibility of exposing sensitive customer data.

For awhile, it was seemingly impossible to server-side render custom elements. Shadow DOM is imperative; you code statements that tell the browser to instantiate a new Shadow Root. This Shadow Root is what provides the ability for custom elements to take advantage of CSS scoping, DOM encapsulation, and composability. While the Shadow DOM specification is powerful, due to its imperative nature, Shadow DOM isn't immediately server-side renderable. Browser specifications aren't natively available in server environments like Node.js. Node.js is built on the V8 JavaScript engine that originated in the Chrome browser, but Node.js lacks browser-specific specifications like the Document Object Model (DOM). If you were going to try to instantiate the `class` that extends `HTMLElement` in a Node.js environment, there would be an error because `HTMLElement` doesn't exist in the context of Node.js, for instance.

The lack of the DOM in Node.js presents an interesting problem when server-side rendering custom elements. All the necessary browser specifications would need to be "shimmed" or "polyfilled" before the custom element `class` could instantiate, then custom logic on the server would need to parse and output a server-side generated template. An npm package that did just that is `@skatejs/ssr`, a package currently in maintenance mode, which was created by Github user [@treshugart](https://github.com/treshugart). `@skatejs/ssr` extended [undom](https://github.com/developit/undom) and brought support for Custom Elements v1 to Node.js. You could use this package to server-side render custom elements built with [Skate](https://github.com/skatejs/skatejs), or with some configuration, custom elements coded directly with browser specifications. This tool generated templates server-side that enabled sites built with custom elements to be SEO friendly and highly performant. `@skatejs/ssr` worked for static-site generation, but it lacked the ability to "hydrate" components. It became apparent to the web development community a specification that enabled server-side rendering was needed. Enter Declarative Shadow DOM.

### Declarative Shadow DOM

Declarative Shadow DOM is a browser specification that enables Shadow Root to be declaratively instantiated in HTML. Looking at the `AppHeader` component you developed in the last chapter, let's see how Declarative Shadow DOM differs. Instead of imperatively declaring a Shadow Root, you can declare the Shadow Root directly on a HTML template using the `shadowroot` HTML attribute. In the example below that abbreviates the necessary styling and HTML template, `<app-header>` tag name is included in a template. Using Declarative Shadow DOM, the direct child of the `AppHeader` is a HTML template. The HTML template includes a Shadow Root with the HTML attribute `shadowroot` set to the `mode` that would have otherwise been imperatively defined via a call to `attachShadow` on the `AppHeader class`. The template includes the CSS styling and HTML for the component.

```html
<app-header>
  <template shadowroot="open">
    <style>
      :host {
        display: flex;
        justify-content: space-between;
        align-items: center;
        height: 100px;
        padding-left: var(--margin-lg);
        padding-right: var(--margin-lg);
        border-bottom: var(--border-default);
      }
    </style>
    <button is="in-button" class="in-button icon logo"></button>
    <a href="/login" class="login-link" hidden>Login</a>
  </template>
</app-header>
```

In the below example, you can compare the Declarative Shadow DOM example above to the imperative style of declaring a Shadow Root you've used to define the template for each component developed in this book.

```typescript
export class AppHeader extends HTMLElement {
  constructor() {
    super();
    const shadowRoot: ShadowRoot = this.attachShadow({ mode: "open" });
    const template = document.createElement("template");
    template.innerHTML = html`
      <style>
        :host {
          display: flex;
          justify-content: space-between;
          align-items: center;
          height: 100px;
          padding-left: var(--margin-lg);
          padding-right: var(--margin-lg);
          border-bottom: var(--border-default);
        }
      </style>
      <button is="in-button" class="in-button icon logo"></button>
      <a href="/login" class="login-link" hidden>Login</a>
    `;
    shadowRoot.appendChild(template.content.cloneNode(true));
  }
}
```