proposal-top-level-await | top-level ` await ` proposal for ECMAScript | Compiler library

for await...of statement is used to iterate through async iterators, and serve returns an async iterator, where each iteration will be a new incoming request.

Is it specific to deno or is it a top-level-await found in this tc39 proposal?

No, it's not specific to Deno and it's a different proposal than top-level await.

Here's a simple example of an asyncIterator that works in browsers too (non-deno exclusive)