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Comment by TazeTSchnitzel | Hacker News Reader

> WebAssembly would have to load and start as quickly as JS.

Wouldn't it already load faster than JS, because it's much less work to compile and doesn't require guessing types?

It's implementation dependent. Most implementations JIT Wasm up front (I think Chakra is the only engine that interprets). So, JS loads faster because almost all engines interpret first (all?).

I think the primarily-AOT compilation strategy we see today is a consequence of many of the initial workloads being frame-based animation where AOT avoids animation stutters. But this is likely to evolve over time as wasm workloads evolve. If and when we see wasm showing up in frameworks in contexts where page-load is the primary concern I can see a more lazy JIT strategy being the right thing and then we'd want to specify some sort of developer knob to control this. But given a pure-JIT approach like Chakra is using, wasm should be able to load code byte-for-byte faster than JS.

WebKit already has a more lazy JIT strategy. From the article being discussed:

"WebKit’s WebAssembly implementation, like our JavaScript implementation, uses a tiering system to balance startup costs with throughput. Currently, there are two tiers to the engine: the Build Bytecode Quickly (BBQ) tier and the Optimized Machine-code Generator (OMG) tier. Both rely on the B3 JIT as their low-level optimizer."

I agree.

Chakra uses a pure JIT approach? I thought they interpret both in JS and Wasm?

Maybe some terminology difference here but what I meant by 'pure JIT' was that, iiuc, Chakra waits until the function is called to even validate it, then warms up in an interpreter and only if the function is hot compiles it in a background thread. I think that's one end of the eager/lazy spectrum that may well be what a category of wasm uses will want.

Is “interpreting” necessarily faster?

Consider also this is perhaps a false distinction. V8 always produces machine code when running JS IIRC. And that code is JITed doesn't mean the entire module is.

V8 used to do this. Now they have a JS interpreter called Ignition.

> V8 always produces machine code when running JS IIRC.

They used to. They stopped doing that because it made initial load too slow...

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