297134 2025-08-08 12:28:50 -0700 Exception (JS value) thrown inside WebAssembly using WebAssembly.JSTag is wrapped into WebAssembly.Exception immediately 2025-08-08 17:52:06 -0700 1 1 1 Unclassified WebKit WebAssembly WebKit Nightly Build Unspecified Unspecified RESOLVED DUPLICATE 297127 InRadar P2 Major --- 1 bashorov webkit-unassigned webkit-bug-importer ysuzuki oldest_to_newest 2135254 0 bashorov 2025-08-08 12:28:50 -0700 So as a result, 1. It's observable inside a wasm module as an instance of WebAssembly.Exception instead of thrown JS value. 2. It's not unwrapped when it crosses wasm-js border, so in JS it is also visible as an instance of WebAssembly.Exception instead of thrown JS value. 2135262 1 ysuzuki 2025-08-08 13:26:16 -0700 Thanks! This will be fixed in bug 297127 2135263 2 ysuzuki 2025-08-08 13:26:21 -0700 *** This bug has been marked as a duplicate of bug 297127 *** 2135265 3 webkit-bug-importer 2025-08-08 13:27:17 -0700 <rdar://problem/157875232> 2135332 4 keith_miller 2025-08-08 16:16:34 -0700 Are you sure 2 is the case? https://webassembly.github.io/exception-handling/js-api/#call-an-exported-function says it is unwrapped back to the underlying JS value when propagating back through JS. I'm pretty sure the bug in https://github.com/WebKit/WebKit/pull/49130 was due to the opposite; we weren't unwrapping the `WebAssembly.Exception` if it had a JSTag for exported functions if it was created and thrown from wasm i.e. `(throw $JSTag someExternref)` What's the case you're seeing 1 in? 2135367 5 bashorov 2025-08-08 17:43:11 -0700 > we weren't unwrapping the `WebAssembly.Exception` (2) is basically saying the same thing 2135369 6 bashorov 2025-08-08 17:46:54 -0700 BTW, I don't see any test for (1) in the PR. Could you please check if it's fixed? 2135370 7 bashorov 2025-08-08 17:52:06 -0700 > What's the case you're seeing 1 in? Case: an exception is thrown inside wasm using JSTag and caught with JSTag inside wasm. Actual: in the catch block, we receive an instance of WebAssembly.Exception wrapping the original JS value, e,g, JS Error. Expected: in the catch block, we receive the original JS value.