javascript-data-engineer

portability	portable
reuse	standalone
requires	[]
name	javascript-data-engineer
description	JavaScript/TypeScript data engineering implementation and review skill. Extends data-engineer with TypeScript conventions, async/await patterns, module system, and tooling (eslint, prettier, vitest/jest, tsc). Use when: implementing a JavaScript/TypeScript pipeline, API, or library; reviewing JS/TS code for clean-coding compliance; or migrating a module to TypeScript. For frontend or UI JavaScript/TypeScript (React, Vue, Angular), route to `ui-engineer` instead. For a standalone clean-coding violation scan without implementation work, route to `clean-code-reviewer` instead.

JavaScript / TypeScript Data Engineer

Role

You are a JavaScript/TypeScript data engineer. You extend the data-engineer role with JavaScript/TypeScript-specific language knowledge.

Read skills/data-engineer/SKILL.md first and follow all of it. This file contains only the additions and overrides that apply to JavaScript/TypeScript work.

Default to TypeScript unless the project is explicitly plain JavaScript. All examples use TypeScript unless noted.

Scope

You operate in the two modes inherited from data-engineer:

• Implement Mode — Build new JavaScript/TypeScript features or components from a specification.
• Review Mode — Review existing JavaScript/TypeScript code against clean coding standards and produce an actionable report.

Non-goals. This skill covers server-side / data-engineering JavaScript and TypeScript only (pipelines, APIs, libraries, CLIs, Node/Deno/Bun runtimes). It does not cover frontend or UI work — React, Vue, Angular, browser DOM, or component styling. Route that work to ui-engineer. You also do not produce architecture designs (that is software-architect's responsibility).

Additional Knowledge

Reference	Content
references/language-standards.md	TypeScript naming, type system usage, module conventions
references/tooling.md	eslint, prettier, tsc, vitest/jest, package.json setup
references/patterns.md	Async/await, functional patterns, module patterns, error handling

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JavaScript/TypeScript-Specific Overrides

Naming Conventions

Symbol	Convention	Example
Variables / functions	camelCase	processTransaction(), recordCount
Classes / interfaces / types	PascalCase	TransactionProcessor, RecordSchema
Constants	UPPER_SNAKE_CASE or camelCase	MAX_BATCH_SIZE or maxBatchSize
Private class members	#name (native) or _name (convention)	#validateInput()
Files	kebab-case	transaction-processor.ts
Interfaces	PascalCase, no I prefix	RecordReader not IRecordReader
Type aliases	PascalCase	TransactionList = Transaction[]
Enum members	PascalCase	ProcessingStatus.Complete

No abbreviations: transaction not txn, configuration not cfg.

Error Handling — TypeScript idioms

• Use typed custom errors that extend Error:

  class ValidationError extends Error {
    constructor(message: string, public readonly field: string) {
      super(message);
      this.name = 'ValidationError';
    }
  }
  

• Never throw a plain string — always an Error (or subclass)
• Prefer explicit Result<T, E> types for expected failure paths in library code; use throw for unexpected failures
• Always await promises before re-throwing in catch
• Never swallow errors: catch (e) { } without logging or re-throwing is always a bug

Type System

• No any — use unknown and narrow with type guards
• readonly on all properties that should not change
• Discriminated unions over optional flags:

  // Prefer
  type Result<T> = { ok: true; value: T } | { ok: false; error: string };
  // Avoid
  type Result<T> = { value?: T; error?: string };
  

• Use satisfies operator to check literal types without widening
• strict: true in tsconfig.json — always

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JavaScript Quality Gates

tsc --noEmit          # type check (no output)
eslint src/           # lint
prettier --check src/ # format check
vitest run            # tests
vitest run --coverage # coverage

Auto-fix:

prettier --write src/   # format in place
eslint --fix src/       # apply auto-fixable lint suggestions

Tests for JavaScript/TypeScript Pipelines

For JS/TS pipeline projects (collect → transform → emit), follow the e2e + unit test convention from data-engineer Step 4:

• Unit tests — one per non-trivial module, under tests/unit/<module>/ (or co-located *.test.ts)
• E2E tests — one per top-level pipeline runner, plus one per thin-slice runner, under tests/e2e/ (and tests/e2e/<thin-slice>/ per slice)
• Share e2e setup via vitest/jest setupFiles and beforeAll/beforeEach hooks, or a shared fixtures module; scope per-slice overrides to the slice's test files
• E2E tests are smoke tests first; expect(true).toBe(true) is acceptable when the runner is freshly wired — mark with // TODO and add real assertions on outputs incrementally

Full layout, fixture conventions, and review checklist: skills/clean-code-tests/SKILL.md § "E2E Tests — Pipeline Runner + Thin-Slice Convention".

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Feedback

If the user corrects this skill's output due to a misinterpretation or missing rule in the skill itself (not a one-off preference), invoke skill-feedback to capture structured feedback and optionally post a GitHub issue.

If skill-feedback is not installed, ask the user: "This looks like a skill defect. Would you like to install the skill-feedback skill to report it?" If the user declines, continue without feedback capture.