Transpile newer syntax

We must support older browsers by Tuesday. Take the ES2022 modules I wrote and transpile them so they run in Internet Explorer 11 and recent Safari. Keep semantics the same, convert optional chaining, nullish coalescing, and class fields, and produce a single ES5 output per entry point with source maps. Run the project’s tests and report any syntax features that need manual polyfills.

Before I deliver the transpiled bundle to QA, make the output readable enough to verify behavior. Highlight where modern features were transformed, annotate places that required helpers or polyfills, and recommend which polyfills are necessary at runtime versus which need feature-detection. Flag any transforms that could degrade performance in older browsers.

My CI shows all tests passing after transpilation, yet customers on older Android browsers see blank screens. I suspect a missing polyfill or a transformed module loader issue. I don’t know which feature is missing in the field and cannot reproduce the exact environment. What should I check first and what quick diagnostic can I add to capture the failing feature on the client?

Every release we forget to include a small polyfill and only discover it from customer reports. It costs us hotfixes and credibility. What workflow change or checklist will reliably catch missing polyfills before release without adding huge bundle weight?