Migrate to TypeScript

[joeyparrish]

This project should migrate to TypeScript. We need to decide how to do this with minimal disruption to the project and to our normal releases.

This will be the top-level issue for tracking this effort and plans for it.

Things to think about:

• Maybe generate Closure externs from .d.ts for dependent projects still using Closure (Does anyone need this?)
• Shaka bundle importable as ES6 module (Export shaka as ES6 module #1509), plus a backward-compatible bundle for CJS/AMD/<script> usage based on current wrapper.template.js
• Classes or interface definitions for Event types (Put custom event definitions into externs #1564)
• A recognizable build system (Consider a third-party build system #1858), see also comment here: Find an alternative to Esprima #8056 (comment)
• Advice here for structuring the project: Find an alternative to Esprima #8056 (comment)

This should also resolve #6017 and make #8056 obsolete.

[MarianoFacundoArch]

+1 Joey

I believe this shift will bring a host of benefits—improved type safety, better tooling, and enhanced code maintainability. Transitioning to TypeScript can also help us catch errors early, streamline our development process, and ultimately lead to a more robust project.
That said, the migration should be approached carefully to minimize disruption. For instance, generating Closure externs from .d.ts could be an effective way to support dependent projects still using Closure. Additionally, maintaining backward compatibility through dual bundles (ES6 and CJS/AMD/) seems like a practical solution, even if it adds some initial complexity.
I’m excited to see how it will improve our project’s structure and reliability.

[avelad]

• Maybe generate Closure externs from .d.ts for dependent projects still using Closure (Does anyone need this?)

Since we're removing Closure, this should be removed too, at least that's my opinion.

[loicraux]

A good time to switch to TypeScript, especially since : https://devblogs.microsoft.com/typescript/typescript-native-port/ 👍🏻