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.

skills.sh installs: 263
GitHub stars: 62
last updated: Aug 21, 2026

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Install

$ npx -y skills add ccheney/robust-skills --skill modern-javascript --agent claude-code

Installs into .claude/skills of the current project.

Files

Modern JavaScript

Keep specification status, runtime support, and toolchain support separate. The user's explicit instructions take precedence over this skill's guidelines.

Work against the target

Use the relevant JavaScript, required behavior, and declared runtime as input. Inspect engines, browser targets, lockfiles, and build configuration as needed for the feature. Do not invent a baseline or upgrade runtimes merely to use newer syntax.

Prefer a supported standardized feature. A proposal can fit when the user/project chooses it and a maintained transform or polyfill implements the required revision. Bundled edition and support tables are dated snapshots; verify changing status against the sources below.