mdjs-viewer is a Chrome extension developed by Thomas Allmer that allows users to execute and view interactive Markdown JavaScript demos directly on GitHub. This extension enhances the functionality of the mdjs (Markdown JavaScript) library and brings it to the GitHub platform.

With mdjs-viewer, users can now see live demos in various places on GitHub, including GitHub Markdown files like README.md and GitHub Issues. The extension ensures security by isolating the execution of user code and implementing measures such as requiring user action before executing any code, running demos within an iframe with sandbox settings, and restricting requests outside of the iframe.

It's worth noting that mdjs-viewer modifies the Content Security Policy (CSP) for GitHub by adding specific rules to the script-src, allowing the execution of code blocks within the mdjs iframe and loading user dependencies from within the iframe.

To use mdjs-viewer, simply enable the extension and visit markdown pages and issues on GitHub. The extension adds a "show demo ▹" button to these pages, which, when clicked, processes the raw markdown text using mdjs and replaces imports with unpkg.com URLs. Finally, an iframe is created to display the mdjs-generated HTML and JavaScript output.

Please note that there is a limit to the number of anonymous API calls to GitHub per hour (60), and requesting the raw content of an issue message requires an API key.

Give mdjs-viewer a try to enhance your GitHub experience with interactive Markdown JavaScript demos!