# `has`

> Contract 2.0.0 · package sha256 `a857eca95b35921109faf997094bb4192f12527d9d0fcd4be7e97f06425bad6e` · generated from `configurator-runtime.d.ts` by `services/onsite-scripter/scripts/build-contract-docs.mjs`; edit the source, not this file.

Function · `import { has } from '@holostep-configurators/runtime-client';` · stable · since 2.0.0 · section 22. Pure helpers (root of the package; run in Node and the fake)

How app code reaches an experimental member: a type guard over [`session.supports(id)`](Session.supports.md). The member
is optional in this declaration, so it compiles only after `has()` returned true for its id.
`if (has(session, 'beforeCommit')) session.beforeCommit('layout', fn)`. Sync.

## Declaration

```ts
export declare function has<S extends Session, K extends keyof CapabilityMembers>(session: S, id: K): session is S & CapabilityMembers[K];
```

## Example

Imports: values (`has`, `validate`, the `Holo*Error` classes, the pure helpers) from `@holostep-configurators/runtime-client`, types from `@holostep-configurators/runtime-client/contract`, `/math` and `/testing` names from those entries; `boot` from the runtime module the root's `loadRuntimeAtFloor` resolves to. A type your page defines is your app's: declare it there, never import it from the package.

Compiled under the contract's strict settings (`examples/declaration/22-has.ts`):

```ts
import { has } from '@holostep-configurators/runtime-client';
import type { Part, ScreenPoint, Session } from '@holostep-configurators/runtime-client/contract';
declare const session: Session;
declare const signal: AbortSignal;
declare const longPress: {
  onFire(cb: (e: { pointerId: number; at: ScreenPoint }, part: Part) => void): void;
};
longPress.onFire((e, part) => {
  if (has(session, 'input.startDrag')) {
    session.input.startDrag(part, { pointerId: e.pointerId, at: e.at });
  } else {
    console.info('long-press drag is not in this runtime');     // a guard, never a crash
  }
});
```

## Generic-API test (spec 3.1)

| Rule | Result |
| --- | --- |
| 1. Neutral name | pass: `has` names no product |
| 2. A precedent | pass: [model-viewer canActivateAR and activateAR()](https://modelviewer.dev/docs/index.html#entrydocs-augmentedreality-methods-activateAR) (row `G66`); [XRSession.end()](https://developer.mozilla.org/en-US/docs/Web/API/XRSession/end) (row `G66`); [Navigator.share() (resolves when the share UI closes)](https://developer.mozilla.org/en-US/docs/Web/API/Navigator/share) (row `G66`) |
| 3. Two apps, or labs | pass: 2 apps (ledger: configurator-template, tryon-template) |
| 4. The cheaper fix first | decided per need in Appendix B: rows `G66` at tier labs (a member only where no rule, data, asset or app code serves the need) |