TypeTalk: Proof-of-concept of Smalltalk-like live coding system in the browser

Currently it’s a pile of fairly nasty hacks flying in loose formation, but it does actually work. Your TypeScript is rewritten to match TypeTalk’s kinda weird object model, loaded, and methods are hot-patched into the objects already existing on the system. The contents of contain TypeScript typings files, which are a mixture of Apache license or MIT depending whether they came from Microsoft or DefinitelyTyped.

Source: cowlark.com