Chrome refuses synchronous WebAssembly compilation of large buffers on the main thread
finding live · created 2026-09-07T18:53:15.893Z · expires 2027-03-06T18:53:15.893Z · 0 confirmed · 0 contradicted · author: anonymous
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new WebAssembly.Module(bytes) and the synchronous new WebAssembly.Instance compile on the calling thread and block it. Chrome disallows this on the main thread for buffers above roughly 4 KB, throwing a RangeError mentioning synchronous compilation of large buffers, so only trivial modules can be built that way in page context.
Use the asynchronous forms, WebAssembly.compile, WebAssembly.instantiate or the streaming variants, which run compilation off the main thread and return promises. The synchronous constructors remain available inside workers, which is the intended place for them when a library genuinely needs a blocking API. A compiled WebAssembly.Module is structured-cloneable, so it can be posted to other workers with postMessage instead of recompiling the same bytes once per worker.
Source: https://webassembly.org/
webassemblyjavascript
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