---
name: handbook-javascript-typescript
description: Use when developing, maintaining, reviewing, diagnosing, configuring, or understanding JavaScript or TypeScript code and project checks.
---

# JavaScript and TypeScript Handbook

This Handbook supplies required understanding for JavaScript and TypeScript
work. It selects reading rather than owning the user's task. Treat the guidance
as supplemental to instructions, requirements, Skills, and project-specific
decisions in the active working directory.

## Select the required reading

1. Resolve every link relative to this `SKILL.md`.
2. For work on JavaScript or TypeScript code, read the complete foundation
   before making dependent design, implementation, diagnosis, or review
   decisions. A direct learning or explanation request about one foundation
   subject may read its matching unit without loading the other one when no
   code artifact work is present.
3. Evaluate every conditional package from the observable work and current
   materials. Read every matching package cumulatively; do not choose only the
   closest match. A direct learning or explanation request about a package's
   subject also matches that package without automatically loading the language
   code-work foundation.
4. Reuse a reading unit that is already loaded, current, and available. Read it
   again when its content changed or after recovery or compaction when its
   necessary basis can no longer be established.
5. Re-evaluate this Handbook and all package conditions when the task phase,
   language, platform, artifact, production method, or available reading basis
   changes. Add newly required reading before dependent work.

This Handbook has no dependency on another Handbook. Continue the user's task
under the applicable Workflow or active-project process after loading and
applying the required understanding.

## Foundation for JavaScript and TypeScript code

For developing, maintaining, reviewing, or diagnosing JavaScript or TypeScript
code, read these complete documents:

- [TypeScript and JavaScript coding principles](../../knowledge/typescript/coding-principles.md)
- [Cohesive JavaScript and TypeScript module organization](../../knowledge/javascript/cohesive-module-organization.md)

## Conditional required-reading packages

### Promise coordination

When coordinating concurrent Promise outcomes or settlement across lifecycle
boundaries, or directly learning or explaining that subject, read
[Coordinating Promise outcomes](../../knowledge/javascript/promises.md) in full.

### Date and time

When working with date or time values, or directly learning or explaining their
JavaScript or TypeScript behavior, read
[JavaScript date and time](../../knowledge/javascript/date-and-time.md) in full.

### TypeScript and ESLint project checks

When establishing, sharing, or diagnosing TypeScript and ESLint checks, or
directly learning or explaining those checks, read these complete documents:

- [Enforcing TypeScript coding principles](../../knowledge/typescript/enforcing-coding-principles.md)
- [Composable ESLint policy rules](../../knowledge/eslint/composable-policy-rules.md)
- [Type-aware ESLint concurrency](../../knowledge/eslint/typed-lint-concurrency.md)

If the same current reading was selected independently for development-tooling
work, reuse it rather than reading a duplicate copy.