/experience-lwc-typescript-migrate

name: experience-lwc-typescript-migrate
description: "Use when converting an existing JavaScript Lightning Web Component (.js, .html, .css) to TypeScript with full type annotations and a matching `.d.ts` file that exposes only the component's `@api` surface. TRIGGER when the user says \"convert LWC to TypeScript\", \"migrate LWC to TS\", \"rename .js to .ts for this component\", \"add types to my LWC\", \"generate .d.ts for this LWC\", \"type-annotate @api properties\", or \"produce declare module 'c/componentName' definitions\". DO NOT TRIGGER when the user is authoring a brand-new LWC from scratch (use experience-lwc-generate), generating Jest tests for an existing LWC (use experience-lwc-generate), or migrating an Aura component to LWC."
metadata:
  version: "1.0"
  relatedSkills:
    - "experience-lwc-generate"
  cliTools:
    - tool: ["git"]
      semver: ">=2.0.0"
    - tool: ["jq"]
      semver: ">=1.6"
    - tool: ["tsc"]
      semver: ">=4.0.0"

<!-- adk-managed-skill -->

Converting LWC to TypeScript

Convert a Lightning Web Component bundle from JavaScript to TypeScript. The deliverable is a fully-typed `.ts` implementation **plus** a `.d.ts` file that only exposes `@api` members (the public surface other LWCs consume).

When to Use This Skill

• User wants to migrate a single component or a folder of components from

`.js` to `.ts`.

• User needs a `.d.ts` for an existing LWC so other components (or an

external TypeScript host) can import it safely.

• User is adding type annotations to an already-renamed `.ts` LWC that

hasn't been properly typed yet.

• User wants JSDoc-style type hints upgraded to real TypeScript types.

Prerequisites

• The component builds and runs correctly in JavaScript today.
• `git` is available (the rename must preserve history via `git mv`).
• A TypeScript compiler is wired into the build (either the SFDX TS

pipeline or a standalone `tsc` step).

---

Workflow

Step 1 — Read the component

Open every file in the bundle:

componentName/
├── componentName.js
├── componentName.html
├── componentName.css
└── (possibly) __tests__/, __utam__/, existing .d.ts

Understand:

• What extends `LightningElement`? What is the class name?
• Which fields and methods carry the `@api` decorator?
• Which properties/methods have existing JSDoc (use as a type hint

starting point, but validate against actual usage — JSDoc lies).

• Which parameters / return types can you infer from how the code is

called internally?

Step 2 — Rename `.js` → `.ts` using `git mv`

git mv componentName/componentName.js componentName/componentName.ts

Repeat for any helper `.js` files in the bundle (unless they're already `.ts`). **Never** plain `mv` — that loses the history link TypeScript reviewers rely on.

Step 3 — Add type annotations in the `.ts`

Apply types in this priority order so you stop as soon as the public contract is solid:

1. **`@api` properties and methods first.** Generate JSDoc if it's missing, then translate JSDoc types to TS syntax (`string`, `number`, `boolean`, `Promise<T>`). Validate each JSDoc claim against the code before trusting it. 2. **Complex shapes become `interface` or `type` aliases** — not inline shapes repeated everywhere. 3. **Optional members use `?`** only when the value is genuinely allowed to be `undefined`. Do not sprinkle `?` defensively. 4. **Private/internal state** — still type it, but don't export the types. Use `private` for members that must never be touched by consumers. 5. **Event handlers** — prefer precise DOM event types:

• `MouseEvent` for `onclick` (and other click-like handlers). `click`

is dispatched as a `MouseEvent` — including keyboard-activated clicks — so typing it as `PointerEvent` would let handlers rely on pointer-only fields (`pointerType`, `pressure`, etc.) that are undefined in those cases.

• `PointerEvent` for `onpointerdown` / `onpointerup` / `onpointermove`

and other `pointer*` handlers where pointer-specific fields are actually meaningful.

• `CustomEvent<{ detail: ... }>` for LWC custom events.
• `Event` is the last resort; document why when using it.

6. **Async methods** always return `Promise<T>` — never bare `T`. 7. **Avoid `any`.** If you genuinely can't type something, use `unknown` and narrow with a type guard.

Reference patterns

Load [[assets/type-patterns.ts|assets/type-patterns.ts]] as an inline example covering property types, method types, and event handler types.

Step 4 — Generate the `.d.ts`

Create `componentName.d.ts` next to the `.ts`. It must:

• Contain **only `@api` members** — no private state, no internal

methods, no lifecycle hooks unless they are themselves `@api`.

• Preserve `@api` JSDoc verbatim (including `@type`, `@required`,

`@default`, `@param`, `@returns` tags) directly above each declaration.

• Declare the LWC module namespace `c/componentName` (or the org's

namespace if different).

Template: load [[assets/dts-template.ts|assets/dts-template.ts]] as the starting `.d.ts` shape.

If the component has **no** `@api` members, still produce the module declaration with a comment explaining there's no public surface — don't skip the file.

Step 5 — Compile and test

• Run the TypeScript compiler (`tsc --noEmit` or the build's equivalent).

Resolve every error before calling it done; no `@ts-ignore` patches.

• Run the component's existing Jest tests. The behavior should be

identical.

• Run the bundled consumer-finder unconditionally — empty output is a

valid result, not a reason to skip. The script resolves the search paths from `sfdx-project.json`'s `packageDirectories` (or falls back to `<project-root>`), rejects any entry that escapes the project root, and performs the LWC-import search internally so the invocation is fully deterministic:

"<skill_dir>/scripts/find-consumers.sh" "<project-root>" "<componentName>"

For ea