With the new Playground, we have a lot more control over the environment in which your code runs. The new Playground is now loosely coupled to both monaco-editor and monaco-typescript which provide the editing experience. https://github.com/microsoft/monaco-editor/ https://github.com/microsoft/monaco-typescript Loosely coupling means the playground supports letting users choose between many different versions of the TypeScript build which monaco-typescript has integrated. We have infrastructure to build a copy of both monaco-editor and monaco-typescript for any version of TypeScript. This means we can now support: - Beta builds of TypeScript - Nightly builds of TypeScript - Pull Request builds of TypeScript - Older builds of TypeScript via https://github.com/orta/make-monaco-builds The foundational architecture for how the new playground supports different versions of TypeScript came from the project which this site is a fork of: https://github.com/agentcooper/typescript-play