# ng-signals-template A minimal Angular 22 starter: signals for state, `resource()` for async data, and a `RemoteData` type that makes "loading but has an error," "success with no value," and similar illegal combinations impossible to construct. One worked feature (`users/`) shows the whole pattern end to end, including a routed, deep-linkable action (click a user → see their details at `/users/:id` → go back). It's extracted from a larger reference app — the "POC" referenced throughout this document — which shows the same ideas grown up to production scale (multi-context DDD, enforced architecture boundaries, i18n, a real design system, generated API clients). This template deliberately keeps only the part of that setup useful from day one, and documents exactly where to reach for the rest as a project grows. ## Running it ```bash npm start # ng serve npm test # ng test (Vitest) npm run test:coverage # ng test --coverage, gated by thresholds in angular.json npm run format:check # prettier --check . npm run build # production build ``` ## Architecture Each business capability is a **context** (`users/`) split into `domain → application → infrastructure`/`ui` layers; dependencies only point inward. `shared/` holds cross-context building blocks, itself layered by atomic-design tier (`atoms → molecules → templates`). This is convention, not lint-enforced yet — see Growth path. ```mermaid flowchart TD subgraph shared["shared/ (cross-context)"] sapp["application/\nremote-data.ts"] sinfra["infrastructure/\nhttp.ts (the only fetch() caller)"] sui["ui/\natoms → molecules → templates"] end subgraph users["users/ (one context)"] udom["domain/\nuser.ts (no Angular import)"] uinfra["infrastructure/\nusers.adapter.ts (parses + type-guards)"] uapp["application/\n*.resource.ts"] uui["ui/\norganisms + page"] end uui --> uapp uapp --> udom uapp --> uinfra uinfra -. uses .-> sinfra uui -. reuses .-> sui uapp -. reuses .-> sapp classDef domain fill:#eef,stroke:#88a class udom,uinfra,uapp,uui domain ``` ### Why so few dependencies The whole app runs on `@angular/core`'s signals + `resource()`, native `fetch`, and `@angular/router` for navigation — nothing else is imported directly. `rxjs` is a peer dependency of `@angular/core` itself and is never imported by this template's own code. `@angular/forms` has been dropped entirely — nothing here used it. ```mermaid flowchart LR app["Your app code"] app -->|imports| core["@angular/core\nsignal · computed · resource"] app -->|calls| fetchApi["native fetch()"] app -->|navigates via| router["@angular/router"] app -.->|"peer dep of @angular/core,\nnever imported directly"| rxjs["rxjs"] app -.->|"never installed —\nzoneless by default"| zonejs["zone.js"] app -.->|"never installed"| ngrx["NgRx / any store lib"] app -.->|"never installed —\nfetch() instead"| http["HttpClient"] classDef used fill:#dfe,stroke:#4a4 classDef avoided fill:#fee,stroke:#a44,stroke-dasharray: 4 4 class core,fetchApi,router used class rxjs,zonejs,ngrx,http avoided ``` ## What's here - **`RemoteData`** (`shared/application/remote-data.ts`) — a 4-variant union (`Loading | Empty | Failure | Success`) plus `fromResource()`, which projects Angular's own `resource()` into one. `Failure` carries the real `Error` — no generic error parameter to instantiate, since Angular's `resource()` only ever fails with an `Error`. No store, no reducer — `resource()` already holds the async state; `RemoteData` just normalizes it for exhaustive rendering. - **``** (`shared/ui/molecules/async.component.ts`) — a `@switch` over all 4 states: a spinner while loading, an empty message, a failure message with a retry button, or your projected content on success. Because `` can't hand data back to its parent, pages narrow the same `RemoteData` value themselves with `@let` before rendering their payload — see `users.page.ts` for the pattern. Reused by both fetches in `users/`. - **``** (`shared/ui/templates/page-shell.component.ts`) — a heading plus one content slot. That's it. - **`users/`** — one feature context, laid out the same way a bigger one would be: `domain/` (pure types, no Angular import), `infrastructure/` (parses and type-guards the raw API response into `User`/`UserDetail`, throwing a typed `HttpError` or `ParseError` on failure — `shared/infrastructure/http.ts` is the only file that calls `fetch` directly), `application/` (composes infrastructure + `resource()` — this is also exactly where a real store would slot in later), `ui/` (organisms + the page). Routing is wired with `withComponentInputBinding()`, so clicking a user navigates to `/users/:id` and the route param binds straight onto the page's `userId` input — no manual signal wiring, and the detail view is deep-linkable: ```mermaid sequenceDiagram participant Page as UsersPage participant Res as usersResource() participant Api as fetchUsers (fetch) participant RD as fromResource() participant Async as app-async participant List as app-user-list participant Router as Router Page->>Res: usersResource() Res->>Api: loader() Api-->>Res: User[] Page->>RD: fromResource(usersResource, isEmptyUserList) RD-->>Async: RemoteData tag (Loading/Empty/Failure/Success) Async->>List: render on Success List->>Router: select.emit(id) → navigate(['/users', id]) Router->>Page: binds userId input from the route Note over Page: template swaps to app-user-detail,
which repeats the same chain via userDetailResource ``` - Path aliases `@shared/*` and `@users/*` (see `tsconfig.json`) instead of relative `../../` imports, one per context — add one per new context you create. - Tests are BDD-style (`describe`/`it`, one `expect` per `it`) and black-box: they assert on rendered DOM and emitted events, never on a component's private fields, so a test never breaks just because an internal was refactored. Routed pages are tested with `RouterTestingHarness` driving real navigation (see `users.page.spec.ts`), not by poking at signals directly. - **Type safety & CI** — `strict` and `strictTemplates` are both on, so `RemoteData`'s "illegal states unrepresentable" claim is actually checked by the compiler, not just a convention. `.github/workflows/ci.yml` runs a format check, the test suite (with coverage thresholds), and a production build on every push and pull request. ## What's deliberately not here (vs. the POC) | Missing | Why | | ---------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | Elm-style store (`createStore`/Model-Msg-reduce) | Not needed until a page's state has more than a couple of interacting fields — see Growth path below. | | i18n (`$localize` + translation file) | POC-specific requirement (a Dutch app shipping English too); irrelevant for a single-locale starter. | | CIBG Huisstijl theming / token bridge | The POC's specific design system; a starter has no house style to vendor yet. | | `dependency-cruiser` boundary enforcement | Real value once you have 2+ contexts that must not import each other; overhead for one. | | `contracts/` layer + generated API client | A hand-written `parse*` boundary already guards the response shape (see `users/infrastructure/users.adapter.ts`); only add codegen once there's a real OpenAPI contract to generate from, not a public test API. | | Linter (`ESLint`/`angular-eslint`) | `strict` + `strictTemplates` + Prettier already catch most of what a linter would here; add one when you have team-specific rules — it's five more devDependencies and a config most teams rewrite anyway. | | Per-environment config (`.env` / `fileReplacements`) | The API base URL is a single exported `const` in `shared/infrastructure/http.ts` — greppable, zero ceremony. Swap for Angular's built-in `fileReplacements` + `src/environments/` when you need per-deploy values. | | Storybook + axe a11y gate | Testing/documentation infrastructure that pays off at a much bigger component count. | ## Growth path — when you outgrow this Each of these is a real, working pattern in the POC — copy it when you actually need it, not before: - **A page's state grows past 2-3 interacting fields, or needs undo/multi-step flow** → add an Elm-style store: `shared/application/store.ts` (`createStore`) + a `*.machine.ts` per feature (Model/Msg/pure `reduce`). See [`docs/adding-a-store.md`](docs/adding-a-store.md) for a step-by-step walkthrough that builds one from scratch using only signals — no new dependencies. - **You have 2+ contexts that must not import each other** → add `dependency-cruiser` (`.dependency-cruiser.js`) to enforce the `domain → application → infrastructure`/`ui` direction this template already follows by convention but doesn't check. - **You're consuming a real backend's OpenAPI contract** → add a `contracts/` layer (wire DTOs) + a generated typed client on top of the hand-written `parse*` boundary already in `infrastructure/` (see `users/infrastructure/users.adapter.ts`, and ADR-0001 / `.claude/skills/bff-endpoint/SKILL.md` if you're working from the POC directly). - **A second locale** → wrap user-facing copy in `$localize` with a stable custom id and add a translation `.xlf` file (see the POC's `CLAUDE.md` "User-facing copy" convention). - **A real design system** → vendor your CSS, then bridge your own token names onto it the way ADR-0003 (`docs/reference/architecture/0003-cibg-huisstijl.md` in the POC) does — keep your token names stable, only their values change. - **Testing/a11y at real component count** → add Storybook + the axe a11y addon so every component's states are visually verifiable and accessibility-checked, not just behavior-tested. ## Folder convention Each business capability is a context under `src/app//`, split into `domain/application/infrastructure/ui` — dependencies point inward (`ui → application → domain`; only `application` reaches `infrastructure`). Inside a context's `ui/`, components are organized by atomic-design layer (`atoms → molecules → organisms → templates → pages`); `shared/` holds only cross-context building blocks. When you add a second context, mirror `users/`'s shape.