Deno does not have its own javascript implementation, it uses the V8 javascript engine, and V8 happens to implement padStart and padEnd.

V8 was originally created as the javascript engine for Chrome, but it is used in many products now, including Node.js and Deno: https://v8.dev/

That’s true for padding. Deno is still doing a lot to standardize on the web platform APIs to be part of the base runtime available and that’s work they’re doing on their own and not for free as part of v8. This is similar to what we do at Cloudflare and I think there’s similar efforts within Node in 17 for what it’s worth.