The answer
Yes. Be able to implement map, filter, reduce, bind, and Promise.all from scratch. Interviewers often ask for polyfills to test your understanding of how these methods work internally.
Top JavaScript Interview Topics for Frontend Developers
Should I be able to implement polyfills for JavaScript interviews?
More FAQs in Top JavaScript Interview Topics for Frontend Developers
Closures, event loop, this keyword, call/apply/bind, promises/async-await, prototypes, debounce/throttle, currying, event bubbling/delegation, polyfills, CORS, and async/defer. Study each deeply and implement from scratch.
Closures are the foundation of many interview questions: data privacy, currying, debounce, throttle, memoize, and the loop closure bug. Understanding closures is essential for almost every JS interview.
Implementing debounce or throttle from scratch (Flipkart, Walmart), polyfills for map/filter/reduce/bind, the event loop output question (sync, microtask, macrotask order), and currying (sum(1)(2)(3) - Amazon).
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