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Modern ES Features — Senior Interview Prep

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Modern ES Features — Senior Interview Prep

The post-ES2020 JavaScript a senior is expected to know on sight. Not “what is let” — the features added 2020-2025 that change how code is written: optional chaining, private fields, top-level await, generators, modern array methods, Temporal, Promise utilities, and the upcoming using resource management.

Files

# Topic
01 Optional chaining, nullish coalescing, logical assignment
02 Private fields, static blocks, decorators
03 Top-level await and dynamic import
04 Iterators and generators (incl. for-await-of)
05 Modern array and object methods
06 Temporal and modern Intl
07 Promise extensions and AbortSignal statics
08 using resource management, weak refs, import attributes

Quick “did you know” inventory

Year Notable
ES2020 optional chaining ?., nullish coalescing ??, BigInt, Promise.allSettled, dynamic import()
ES2021 logical assignment ??=/||=/&&=, String.replaceAll, Promise.any, WeakRef/FinalizationRegistry
ES2022 top-level await, private fields #x, static class blocks, at() on Array/String, Object.hasOwn, cause on Error
ES2023 immutable array methods (toSorted/toReversed/toSpliced/with), findLast/findLastIndex
ES2024 Promise.withResolvers, Object.groupBy/Map.groupBy, Atomics.waitAsync, ArrayBuffer.prototype.transfer, Array.fromAsync
Stage 3/4 (rolling) Temporal, decorators, import attributes (with), using/await using, set methods

For your tsconfig target, ES2022 is a safe modern default; ES2023 if your support matrix allows.

Cross-references