javascript-patterns
Skill2 starsChanged 7 days agoMITView on GitHub
JavaScript language patterns for modern syntax, async handling, ESM/CJS module systems, error handling, and review checklist, with or without TypeScript on top. Use whenever the project contains `.js`/`.mjs`/`.cjs`/`.jsx` files or a `package.json`, OR the user asks about JavaScript, its async model, its module system, or its package tooling, even if "JavaScript" is not mentioned by name.
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The file
We split this skill into the rules it gives an agent
2 rules. About 0 are common, 1 is distinctive, and 1 is very specific to this project.
≈0
Common · estimate
Many files like this have a rule of this kind.
≈1
Distinctive · estimate
This author's own choices. Worth a look.
1
Very specific
Tied to their project's names, files or tools. Probably skip.
- Common
- Distinctive
- Very specific
- Very specific: line 8
Default assumption: a project running on the current Node.js Active LTS (Node 24, "Krypton") or a modern browser baseline.
- Distinctive: line 10
If the project also uses TypeScript, the type-aware skill applies on top of these language patterns.
≈ “Common” is an estimate: at least 1 in 5 of the 350,495 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.
Files
JavaScript patterns
Default assumption: a project running on the current Node.js Active LTS (Node 24, "Krypton") or a modern browser baseline.
- If the project also uses TypeScript, the type-aware skill applies on top of these language patterns.
- Adapt advice to the Node version in the project's
.nvmrc,.tool-versions, orenginesfield inpackage.json.
Reference files
| File | Covers |
| reference/modules.md | ESM and CJS, package.json "type", dynamic import(), dual-package hazard |
| reference/syntax.md | Modern syntax: optional chaining, nullish coalescing, logical assignment, at() |
| reference/async.md | async/await, Promise.*, for await...of, top-level await |
| reference/errors.md | Error subclasses, Error.cause, unhandled rejection, using (advisory) |
| reference/equality-and-numbers.md | ===, Number.isNaN, Array.isArray, IEEE 754, BigInt |
| reference/collections.md | Map, Set, WeakMap, WeakSet and when to reach for each |
| reference/jsdoc.md | // @ts-check plus JSDoc tags for editor-checked types in .js files |
| reference/anti-patterns.md | Twelve review-time anti-patterns with severity calls |
References
- MDN JavaScript reference: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference
- Node.js packages: https://nodejs.org/api/packages.html
- Node.js ESM: https://nodejs.org/api/esm.html
- Node.js process: https://nodejs.org/api/process.html
- Node.js previous releases (LTS schedule): https://nodejs.org/en/about/previous-releases
- TC39 proposals: https://github.com/tc39/proposals
- 2ality (Axel Rauschmayer): https://2ality.com/
- You Don't Know JS, 2nd ed. (Kyle Simpson): https://github.com/getify/You-Dont-Know-JS
Version notes
Checked: 2026-09-26 against https://nodejs.org/en/about/previous-releases and https://github.com/tc39/proposals
- Node 26 is Current (2026-05); Node 24 "Krypton" is Active LTS (2025-05). Default assumption above stays on the LTS.
- Explicit resource management (
using/await using) reached Stage 4 in 2026;reference/errors.mdupdated, oldtry/finallyadvice kept as Legacy. @satisfiesJSDoc tag: TS 4.9+, unchanged.
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