Safari 27 rewrites module loader in C++ to fix top-level await ordering bugs

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Apple's WebKit team has completely rewritten Safari's JavaScript module loader in Safari 27, replacing a legacy self-hosted JavaScript implementation with C++ code that directly mirrors the ECMAScript specification. The original loader dated back to the abandoned WHATWG Loader proposal from around 2016, predating async/await, which made correctly supporting the ECMAScript 2022 top-level await feature structurally difficult. As a result, modules using top-level await could resolve out of order in Safari, causing intermittent errors such as bindings being accessed before initialization. Engineer Kai Tamkun documented the rewrite in a September 2, 2026 WebKit blog post, noting the team validated the new loader using fuzzing, cross-engine output comparisons, and the test262 and Web Platform Tests suites. The fix is focused on correctness rather than performance, and primarily benefits developers who have encountered top-level await ordering issues specific to Safari.

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