Sandpack

DON'T USE THIS YET!

A bundler that completely works in the browser and takes advantage of it.

Why?

Online code playgrounds are getting more popular: they provide an easy way to play with code without installation. Until a year ago it was very hard to play with bigger web applications in the browser; there was no bundler that was comparable with local bundlers and worked in the browser.

CodeSandbox came along, and still had a pretty basic bundler. However, as CodeSandbox got more popular its bundler got more advanced. Nowadays the bundler is used for all kinds of bigger web projects, and it would be a shame if others couldn't use the functionality.

This library acts as an interface with the bundler of CodeSandbox. It allows you to run any code on a web page, from Vue projects to React projects to Parcel projects. With everything that CodeSandbox supports client side as well.

So what can this bundler do?

This is a list of features that the bundler supports out of the box, the list may be outdated.

1. Hot Module Reloading API (module.hot)
2. npm dependencies
3. Most common transpilers (vue, babel, typescript, css, scss, less, stylus, parcel, etc...)
4. Parallel transpiling
5. On-demand transpiler loading
6. Webpack loader syntax (!raw-loader!./test.js)
7. Friendly error overlay (using create-react-app overlay)
8. Transpilation result caching
9. HTML/CSS entry points

Example usage

This repo serves as an interface to communicate with the bundler. The bundler itself is hosted on sandpack-{version}.codesandbox.io and is heavily cached by a CDN. We also included the necessary files under sandpack if you want to host the bundler yourself.

Using the Manager

The Manager is a class implementation, you can use it by importing Manager.

import { Manager } from 'sandpack';

// There are two ways of initializing a preview, you can give it either an
// iframe element or a selector of an element to create an iframe on.
const manager = new Manager(
  '#preview',
  {
    files: {
      '/index.js': {
        code: `console.log(require('uuid'))`,
      },
    },
    entry: '/index.js',
    dependencies: {
      uuid: 'latest',
    },
  } /* We support a third parameter for advanced options, you can find more info in the bottom */
);

// When you make a change you can just run `updatePreview`, we'll automatically discover
// which files have changed and hot reload them.
manager.updatePreview({
  files: {
    '/index.js': {
      code: `console.log('New Text!')`,
    },
  },
  entry: '/index.js',
  dependencies: {
    uuid: 'latest',
  },
});

If you specify a package.json in the list of files we will use that as source of truth instead, we infer dependencies and entry from it:

// We infer dependencies and the entry point from package.json
const PACKAGE_JSON_CODE = JSON.stringify(
  {
    title: 'test',
    main: 'index.js',
    dependencies: {
      uuid: 'latest',
    },
  },
  null,
  2
);

// Give it either a selector or an iframe element as first argument, the second arguments are the files
const manager = new Manager('#preview', {
  files: {
    '/index.js': {
      code: `console.log(require('uuid'))`,
    },
    '/package.json': {
      code: PACKAGE_JSON_CODE,
    },
  },
});

SandboxInfo Argument

The second argument in the constructor of Manager is all sandbox info. It has this structure:

{
  /**
   * Files, keys are paths.
  **/
  files: {
    [path: string]: {
      code: string
    }
  },
  /**
   * Dependencies, supports npm and GitHub dependencies
  **/
  dependencies?: {
    [dependencyName: string]: string
  },
  /**
   * Default file to evaluate
  **/
  entry?: string,
  /**
   * The sandbox template to use, this is inferred from the files and package.json if not specified
  **/
  template?: string
}

Options Argument

The third argument in the constructor of Manager is extra options. It has this structure:

{
  /**
   * Location of the bundler. Defaults to `sandpack-${version}.codesandbox.io`
   */
  bundlerURL?: string;
  /**
   * Width of iframe.
   */
  width?: string;
  /**
   * Height of iframe.
   */
  height?: string;
  /**
   * If we should skip the third step: evaluation. Useful if you only want to see
   * transpiled results
   */
  skipEval?: boolean;
}

Manager functions

The manager instance has several helper functions you can call.

updatePreview

Send new sandbox info, like files and dependencies, to the preview. It will automatically hot update the preview with the new files and options. Accepts a single argument sandboxInfo of type SandboxInfo.

updateOptions

Updates the given options and updates the preview. Accepts a single argument options of type Options.

dispatch

Dispatch an event to the sandbox preview and all other listeners. Accepts a single argument, which is the data to send. This is used heavily by the manager and react-sandpack to communicate with the bundler.

getCodeSandboxURL

Create a sandbox from the current files and return an object in this form:

{
  sandboxId: sandbox_id,
  editorUrl: `https://codesandbox.io/s/${sandbox_id}`,
  embedUrl: `https://codesandbox.io/embed/${sandbox_id}`,
}

Why is the bundler hosted externally and not a simple import?

We have three reasons to host the bundler of sandpack externally:

Security

The bundler evaluates and transpiles all files in an iframe under a different subdomain. This is important, because it prevents attackers from tampering with cookies of the host domain when evaluating code.

Performance

We heavily make use of Web Workers for transpilations. Almost all our transpilation happens in web workers, and there is no easy way yet to bundle this in a library.

Bundle Size

Another reason to host the bundler externally is because of code splitting: we split all our transpilers away and load them on-demand. If a user doesn't use sass we won't load the transpiler. This wouldn't be possible if we would give one big JS file as the library.

Offline Support

We use Service Workers to download all transpilers in the background, so the next time a user visits your website they don't have to download the bundler anymore and it can be used offline. This is possible because we host the service worker externally.

I want to highlight that you can also host the bundler by yourself, all necessary files are in the sandpack folder.

Open In CodeSandbox

We show an "Open in CodeSandbox" button in the sandbox preview on the bottom right. This button allows everyone to create a sandbox from the code in the preview, open it in CodeSandbox and share their work more easily with others.