playground-elements

Serverless coding environments for the web.

















Overview
• Getting Started
• Project files
• Module resolution
• TypeScript
• Hiding & Folding
• Custom layouts
• Extending the editor
• Bundling
• Sandbox security
• Components
• Styling
• Syntax highlighting
• Contributing
• FAQ

Overview

Playground Elements are a set of components for creating interactive editable
coding environments on the web, with live updating previews. You can use
Playground Elements to:

- Embed editable code examples in your documentation.
- Build interactive tutorials and example galleries.
- Build full-featured coding sandboxes (think Glitch or JSBin).

#### 🤯 No backend required

Unlike other coding environments, Playground never sends code to a backend
server. Instead, Playground uses a Service
Worker to
create a virtual URL-space that runs 100% within the browser. If you can host
static files, you can host a Playground.

#### TypeScript support

Playground automatically compiles .ts files using TypeScript, and
automatically fetches typings for your imports in order to display errors.
Compilation happens in a Web Worker on a separate thread, so your page stays
responsive.

#### 🧩 Web Components

Playground uses Web Components, so it doesn't require a framework. But it will
play nicely with any framework you're already using, like React, Vue, and
Angular.

#### 🍱 Mix-and-match for flexible layout

Playground is broken up into small components like an editor, file picker, and
preview. Mix-and-match components to create any layout you want, or just use
for an easy out-of-the-box experience.

#### 🎨 Themable

Playground is fully themeable with CSS Custom Properties, down to the color of
each kind of syntax-highlighted token. You can import themes from VSCode using
the configurator, and it
comes with a number of presets too.

---

Try the demo and configurator!

---

Getting Started

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Install from NPM:

``sh
npm i playground-elements
`

`html
type="module"
src="/node_modules/playground-elements/playground-ide.js"
>
`

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Create a element in your HTML, and specify your project files
inline:

`html





`

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Use a server like
@web/dev-server to handle
bare module import resolution automatically:

`sh
npm i -D @web/dev-server
npx web-dev-server --node-resolve --watch
`

Or, use a tool like Rollup to resolve bare
module imports to paths at build time. If you need more help with building and
serving, check out the Modern Web Guides.

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Playground is supported by all modern browsers. It requires support for custom
elements, JS modules, service workers, and web workers.

    Supported:    Chrome
   
Firefox
   
Safari
   
Edge

Unsupported:   Internet Explorer

Project files

There are 3 ways to specify the files of a playground project:

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Add one or more tags within your source as </script>.

`html





`

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Set the project-src attribute or projectSrc property to a JSON file with format:

| Property | Description |
| ------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| files | An object mapping filenames to file data. |
| files.content | Optional text content of the file. If omitted, a fetch is made to retrieve the file by filename, relative to the manifest URL. |
| files.contentType | Optional MIME type of the file. If omitted, type is taken from either the fetch response Content-Type header, or inferred from the filename extension when content is set. |
| files.label | Optional label for display in playground-tab-bar. If omitted, the filename is displayed. |
| files.hidden | If true, the file won't be visible in playground-tab-bar. |
| files.selected | If true, this file's tab will be selected when the project is loaded. Only one file should have this field set. |
| extends | Optional URL to another JSON config file to extend from. Configs are deeply merged. URLs are interpreted relative to the URL of each extendee config. |
| cdnBaseUrl | Optional URL for the underlying npm CDN base url. Confirmed tested are htts://unpkg.com and https://cdn.jsdelivr.net/npm |

`html

`

`json
{
"files": {
"index.html": {},
"typescript.ts": {
"content": "console.log('hello');"
},
"javascript.js": {
"contentType": "text/javascript"
},
"styles.css": {
"label": "Style"
}
}
}
`

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In JavaScript, directly set the config property to an object. The format is
identical to the JSON config file.

`js
const ide = document.querySelector('playground-ide');
ide.config = {
files: {
'index.html': {},
'typescript.ts': {
content: "console.log('hello');",
},
},
};
`

If both project-src and config are set, then the one set most recently has
precedence. When either are set, inline scripts are ignored.

Module resolution

By default, bare module specifiers in JavaScript and TypeScript files are
transformed to special ./node_modules/ URLs, and fetched behind-the-scenes
from unpkg.com by default at the latest version.

`js
// What you write:
import {html} from 'lit';

// What playground serves:
import {html} from './node_modules/lit@2.0.2/index.js';

// What playground fetches behind-the-scenes unless you set cdnBaseUrl:
// https://unpkg.com/lit@latest
`

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To customize the version of a module you import, create a file called
package.json in your project containing a
dependencies
map. This works exactly like it does when using NPM locally.

`json
{
"dependencies": {
"lit": "^2.0.2"
}
}
`

> TIP: Use the hidden attribute or
> property to hide the package.json file from
> being displayed in the list of project files, if you don't want the end-user
> to be able to see or modify it.

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Playground supports Node-style export
conditions when
resolving modules in dependencies, and sets the following
conditions:
module, import, development, and browser.

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For full control over module resolution, you can configure an _import map_. You
may want to do this to change CDNs or point to a locally served copy of a
module:

`js
{
"files": { ... },
"importMap": {
"imports": {
"lit": "https://cdn.skypack.dev/lit@^2.0.2",
"lit/": "https://cdn.skypack.dev/lit@^2.0.2/"
}
}
}
`

When using inline project files, you can specify your import map like so:

`html


...

`

If an import map is defined, but does not contain an entry for a bare module,
then playground defaults to the unpkg.com URL unless cdnBaseUrl is set.

TypeScript

Playground automatically compiles .ts, .tsx, and .jsx files using
TypeScript.

The following compiler settings are used:

| Name | Value |
| ------------------------------------------------------------------------------------------ | ---------- |
| target | es2021 |
| module | esnext |
| moduleResolution | nodenext |
| experimentalDecorators | true |
| allowJs | true |
| jsx | react |

Note that when you import from another project module, the import
statement should use the .js extension (the same as you would do when running
tsc locally):

`ts
import './my-other-module.js';
`

You may also include any Definitely Typed (@types) packages for type checking
during compilation by listing it as a dependency in the project's
package.json file.

Hiding & folding

If a region of code in a Playground project file is surrounded by
playground-hide and playground-hide-end comments, then that region won't be
visible or editable by the user, but it will still be compiled and served.

Similarly, if a region is surrounded by playground-fold and
playground-fold-end comments, then the region will be replaced with a … that
expands to reveal the original editable code when clicked.

Use these special regions to help users focus on a particular part of a file, by
de-emphasizing boilerplate or unrelated code.

#### JavaScript fold example

Note that JavaScript // style comments are not supported.

`ts
/ playground-fold /
import {html, LitElement} from 'lit';
/ playground-fold-end /

class MyElement extends LitElement {
render() {
return htmlHello !;
}
}
/ playground-fold /

customElements.define('my-element', MyElement);
`

Result:

#### HTML hide example


`html







World



`

Result:

#### Disabling

Hiding and folding is enabled by default, but can be disabled by setting the
pragmas property to "off" (disabled with comments hidden) or "off-visible"
(disabled with comments visible). The pragmas property is available on ide,
file-editor, and code-editor.

Custom layouts

provides a complete out-of-the-box experience that's a good
start for many use-cases, but you can mix-and-match the various Playground
sub-components to make your custom layouts.

For example, say we need a layout with an editor above, a preview below, and
only one particular file from the project visible — like this:

To do this, first import just the components you need. The main
playground-elements import loads all Playground elements, but when making a
custom layout it's a good idea to only load the sub-components you're actually
using. This will make your JavaScript bundle smaller.

`html

`

Next create a , with some inline project files. We could also
write our project files separately, and specify them in a JSON manifest. This
project element manages the virtual file system, and coordinates with the
Playground workers. We give it a unique id, which we'll use to connect up the
editor and preview.

`html





`

Next create an editor and preview. Connect both to the project by setting the
property attribute to the project element's id. We could also directly set
the project _property_ to the project element, if we were using JavaScript.

By setting the filename attribute on the editor, we've pinned it to one
particular file. Since we didn't include a , there's no
way for the user to see or switch to other files in the project.

`html



`

Finally, add a little style:

`html

`

Extending the editor

Playground's code editor is built on CodeMirror 6, and can be extended with any CodeMirror extension. This allows for deep customization of the editor's behavior, such as adding new themes, keymaps, autocompletion sources, and more.

There are two ways to apply extensions: programmatically and declaratively.

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The , , and components all have an extensions property which accepts a CodeMirror Extension object (or an array of them).

`js
import {EditorView} from '@codemirror/view';

const ide = document.querySelector('playground-ide');
const myTheme = EditorView.theme({
'&': {
backgroundColor: 'lightpink',
},
});
ide.extensions = myTheme;
`

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For simpler use-cases, or for when you want to package an extension as a reusable HTML element, you can use declarative extensions.

A declarative extension is a custom element that provides one or more CodeMirror extensions. Playground elements will automatically find any declarative extension elements placed in their extensions slot and apply them.

Here's an example of a custom theme packaged as a declarative extension:

`html





`

The codemirrorExtensionMixin handles the communication with the playground editor. Your class just needs to implement the getExtensions() method.

Bundling

Playground uses a Web
Worker
to perform TypeScript compilation. If you are bundling or otherwise modifying
the layout of the playground-elements NPM package, you may need to add special
handling for this file.

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Use the Rollup
@web/rollup-plugin-import-meta-assets
plugin to automatically copy the worker script into the correct location. See
examples/rollup
for an example configuration.

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Webpack 5+ automatically supports loading Web
Workers with no additional plugins.
See
examples/webpack
for an example configuration.

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If you are bundling in another way, you'll need to configure your build so that
the file node_modules/playground-elements/playground-typescript-worker.js is
copied into the same directory as your bundle.

For example, if you bundled playground elements into ./js/app.js, then you
should copy the worker module to ./js/playground-typescript-worker.js.

Sandbox security

> ⚠️ Changing the sandbox base URL from the default can create a security
> vulnerability for your site if not done carefully. Do not change the default
> unless you have a specific reason to, and please read this entire section
> carefully.

The sandboxBaseUrl property and sandbox-base-url attribute can be used to
override the origin where untrusted code will execute when displaying Playground
previews. The default origin is unpkg.com, which is secure because it is
unprivileged and cannot modify the host window.

You may wish to override this default sandbox base URL if you do not want a
dependency on unpkg.com, e.g. for isolation from outages, or because your
network does not have access to it. Note that Playground currently also uses
unpkg.com by default (unless you set cdnBaseUrl) to retrieve imported bare
modules that are not otherwise handled by an import map,
so to remove the dependency on unpkg, you should also set cdnBaseUrl. See the
API docs for more info.

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Playground previews work by using a service
worker.
This service worker takes control over requests to a particular URL space,
allowing it to respond to HTTP requests using the files from your local project,
instead of from a remote server. The playground preview component contains an