Modern Javascript

This is your reference guide for everything ES6 through ES2025, organized around the actual decisions you make while coding. The decision trees are genuinely useful: which array method, how to handle nullish values, when to mutate versus copy. It covers the new immutable array methods like toSorted() and toReversed(), Object.groupBy() from ES2024, optional chaining, nullish coalescing, and all the async patterns you actually use. The before/after examples make it dead simple to spot legacy patterns during refactoring. If you're still writing arr[arr.length - 1] instead of arr.at(-1) or manually grouping arrays with reduce, this will modernize your muscle memory fast.