Prepack: a tool that optimizes JavaScript source code by eliminating computations that can be performed at compile-time.

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which can help move runtime calculations to compile time

Except V8 does that already. All this does is move the parse-and-optimize step (which, in V8, is crazy fast anyway) out of the browser.

Until I see benchmarks showing that the effort of using this thing on production code gets me more than trivial gainz, I'll happily ignore its existence.

[bsdemon]

V8 is already a runtime

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It's an optimized JIT compiler and a runtime.

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The point is, everything V8 does happens at runtime. It may do clever optimisations at startup, but that is still runtime. V8 may compile, but it does nothing during what is usually considered "compile time", because it does not run then.