Microsoft rewrote the TypeScript compiler in native code and made it 10x faster
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So we can make an estimate on how much waste all the fancy web technologies actually cause. That said, even on desktop and smartphones, web technologies are still on the rise. Not really sustainable.
This is about the compiler, not the runtime.
It's obviously the expression of a symptom how the world today designs systems (whether a compiler or a runtime) and how they could be improved if sustainability really was a concern.