Dawn of the Transpiler

The term "transpiler" (referring to a source-to-source translation tool, or "translating compiler") gained popularity around 2013 with the proliferation of translators from TypeScript and other abstractions (CoffeeScript, Dart) into JavaScript.  

JavaScript at the time was becoming a "universal runtime".

Babel is a popular transpiler. tsc is the official transpiler. It can be installed via npm.

TypeScript in CodePen

Can you do TypeScript in CodePen?  

The question is valid as CodePen reveals three containers, one for HTML, one for CSS and one for JavaScript, in its default interface.

To enable TypeScript input, go to Settings, select JavaScript preprocessor and choose TypeScript. Other available preprocessors are LiveScript, CoffeeScript (billed as a "simple and elegant way" to write JavaScript) and Babel.

Note that CodePen will run TypeScript without type-checking errors blocking execution.