building-a-html-element-sandbox-with-lit
Learn how to build a Lit web component to create a dynamic HTML element sandbox with live updates, perfect for experimenting with and showcasing web components.
What this skill does
# Building a HTML Element Sandbox with Lit
In this article I will go over how to set up a [Lit](https://lit.dev/) web component and use it to create a HTML Element sandbox that can be used to update a live component.
> **TLDR** The final source [here](https://github.com/rodydavis/html-element-sandbox) and an online [demo](https://rodydavis.github.io/html-element-sandbox/).
## Prerequisites
* Vscode
* Node >= 16
* Typescript
## Getting Started
We can start off by navigating in terminal to the location of the project and run the following:
```
npm init @vitejs/app --template lit-ts
```
Then enter a project name `html-element-sandbox` and now open the project in vscode and install the dependencies:
```
cd html-element-sandbox
npm i lit
npm i -D @types/node
code .
```
Update the `vite.config.ts` with the following:
```
import { defineConfig } from "vite";
import { resolve } from "path";
export default defineConfig({
base: "/html-element-sandbox/",
build: {
lib: {
entry: "src/html-element-sandbox.ts",
formats: ["es"],
},
rollupOptions: {
input: {
main: resolve(__dirname, "index.html"),
},
},
},
});
```
## Template
Open up the `index.html` and update it with the following:
```
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<link rel="icon" type="image/svg+xml" href="/src/favicon.svg" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>HTML Element Sandbox</title>
<script type="module" src="/src/html-element-sandbox.ts"></script>
<style>
body {
margin: 0;
padding: 0;
font-family: sans-serif;
}
html-element-sandbox {
display: block;
width: 100%;
height: 100vh;
}
</style>
</head>
<body>
<html-element-sandbox>
<template>
<button
class="button"
knob-text="label"
knob-css-color="fg-color"
knob-css-background-color="bg-color"
knob-css-border-radius="shape"
knob-css-font-size="text-font-size"
knob-css-padding="padding"
knob-css---shadow-color="shadow"
>
My Button
</button>
<style>
.button {
--shadow-color: #000;
--elevation: 3px;
display: block;
width: 100%;
height: 100%;
border: none;
background-color: transparent;
cursor: pointer;
box-shadow: 0 var(--elevation) calc(var(--elevation) * 2) 0 var(--shadow-color);
}
</style>
</template>
<div slot="knobs">
<knob-string id="label" name="Label" value="BUTTON"></knob-string>
<knob-group name="Style" expanded>
<knob-color
id="bg-color"
name="Background Color"
value="#ff0000"
></knob-color>
<knob-color
id="fg-color"
name="Foreground Color"
value="#ffffff"
></knob-color>
<knob-color
id="shadow"
name="Shadow Color"
value="#000000"
></knob-color>
<knob-number
id="text-font-size"
name="Font Size"
value="16"
suffix="px"
></knob-number>
<knob-number
id="shape"
name="Border Radius"
value="100"
suffix="px"
></knob-number>
<knob-number
id="padding"
name="Padding"
value="12"
suffix="px"
></knob-number>
</knob-group>
</div>
</html-element-sandbox>
</body>
</html>
```
Here we are defining the markup we want to use in our sandbox. We are using the `html-element-sandbox` component to create a sandbox for our HTML Element.
```
<html-element-sandbox></html-element-sandbox>
```
Each knob is defined by an `id` and a `name`. The `id` is used to identify the knob in the `template` and the `name` is used to display the knob in the UI.
```
<knob-number
id="shape"
name="Border Radius"
value="30"
suffix="px"
></knob-number>
```
For the element inside the `template` we use `knob-*` attributes to get the values of the knobs and set the attributes, CSS style or text content.
```
<!-- Attributes -->
<div knob-attr-disabled="disabled"></div>
<knob-boolean id="disabled" name="Disable" value="false"></knob-boolean>
<!-- CSS Properties -->
<div knob-css-color="fg-color" knob-css-background-color="bg-color"></div>
<knob-color id="bg-color" name="Background Color" value="#ff0000"></knob-color>
<knob-color id="fg-color" name="Foreground Color" value="#ffffff"></knob-color>
<!-- Text Content -->
<div knob-text="content"></div>
<knob-string id="content" name="Text Content" value="Hello World"></knob-string>
```
A single knob can point to multiple elements:
```
<html-element-sandbox>
<template>
<div id="buttons">
<button
knob-text="label"
knob-css-color="fg-color"
knob-css-background-color="bg-color"
knob-css-border-radius="shape"
knob-css-font-size="text-font-size"
knob-css-padding="padding"
knob-css---shadow-color="shadow"
knob-attr-raised="raised"
knob-attr-contenteditable="contenteditable"
></button>
<mwc-button
knob-attr-label="label"
knob-css---mdc-theme-on-primary="fg-color"
knob-css---mdc-theme-primary="bg-color"
knob-css---mdc-shape-small="shape"
knob-attr-raised="raised"
label="My Button"
></mwc-button>
</div>
<script type="module">
import "https://www.unpkg.com/@material/[email protected]/mwc-button.js?module";
</script>
<style>
button {
--shadow-color: #000;
--elevation: 3px;
display: block;
border: none;
background-color: transparent;
cursor: pointer;
box-shadow: 0 var(--elevation) calc(var(--elevation) * 2) 0 var(--shadow-color);
}
mwc-button {
--mdc-theme-on-primary: #000;
--mdc-theme-primary: #fff;
--mdc-shape-small: none;
}
#buttons {
display: flex;
flex-direction: column;
justify-content: center;
align-items: center;
gap: 1rem;
}
</style>
</template>
<div slot="knobs">
<knob-string id="label" name="Label" value="BUTTON"></knob-string>
<knob-group name="Style" expanded>
<knob-color
id="bg-color"
name="Background Color"
value="#ff0000"
></knob-color>
<knob-color
id="fg-color"
name="Foreground Color"
value="#ffffff"
></knob-color>
<knob-color id="shadow" name="Shadow Color" value="#000000"></knob-color>
<knob-number
id="text-font-size"
name="Font Size"
value="16"
suffix="px"
></knob-number>
<knob-number
id="shape"
name="Border Radius"
value="30"
suffix="px"
></knob-number>
<knob-number
id="padding"
name="Padding"
value="12"
suffix="px"
></knob-number>
</knob-group>
<knob-group name="Attributes" expanded>
<knob-boolean id="raised" name="Raised" value="false"></knob-boolean>
<knob-list id="contenteditable" name="Content Editable" value="false">
<option value="true">true</option>
<option value="false">false</option>
</knob-list>
</knob-group>
</div>
</html-element-sandbox>
```
A `style` and `script` can be added to load extra content into the sandbox (e.g. a `script` to load a web component).
## Web Component
Before we update our component we need to rename `my-element.ts` to `html-element-sandbox.ts`
Open up `html-element-sandbox.ts` and update it with the following:
```
import { css, html, LitElement } from "lit";
import { cRelated in Design
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