Polyfills and API Implementation Questions

Practical skills for implementing polyfills and correctly matching Web and language API semantics when platform features are missing. Candidates should know common JavaScript features that are polyfilled such as array iteration and transformation methods, promise behavior, object utilities, and iterable conversion functions. The topic includes deciding when to polyfill versus transpile, performing feature detection, consulting the Mozilla Developer Network and the ECMAScript specification to match edge case behavior, avoiding global namespace pollution, writing idempotent shims, evaluating performance and bundle size trade offs, using polyfill libraries and services responsibly, and testing polyfills across target browsers and environments. Also covered are progressive enhancement strategies, fallback patterns, and maintaining compatibility with versions and standards.