Function declareExperimentalWebMcpTool

packages/core/src/webmcp/declare_tool.ts:32–82

(tool: ToolDescriptor<InputSchema>, injector?: Injector)

 * @experimental
 */
export async function declareExperimentalWebMcpTool<
  const InputSchema extends JsonSchemaForInference,
>(tool: ToolDescriptor<InputSchema>, injector?: Injector): Promise<void> {
  // SSR may not have a document yet, so we abort before checking it.
  if (typeof ngServerMode !== 'undefined' && ngServerMode) return;

  // modelContext was moved from `navigator` to `document` in the spec, but we check both for compatibility with different environments.
  const modelContext =
    (globalThis.document as {modelContext?: ModelContext}).modelContext ??
    (globalThis.navigator as unknown as {modelContext?: ModelContext}).modelContext;

  // Verify WebMCP is supported in this client. The typeof check guards against
  // DOM clobbering (e.g. <form id="modelContext">), which would produce a truthy
  // Element instead of a ModelContext object.
  if (!modelContext || typeof modelContext.registerTool !== 'function') return;

  if (typeof ngDevMode !== 'undefined' && ngDevMode) {
    if (!injector) assertInInjectionContext(declareExperimentalWebMcpTool);
  }

  // Inject the `DestroyRef` and `Injector` immediately, so if it fails we abort
  // before causing any side effects.
  const currentInjector = injector ?? inject(Injector);
  const destroyRef = currentInjector.get(DestroyRef);

  // Wrap the input tool with an `AbortSignal` which aborts when the
  // injection context is destroyed.
  const abortCtrl = new AbortController();
  const wrappedTool: ToolDescriptor<InputSchema> = {
    ...tool,
    execute: (args, client) => {
      // TODO: `@mcp-b/webmcp-polyfill` currently lacks `AbortSignal` in its mock client.
      // Remove the optional chaining when it is updated to match Chrome 153 spec.
      const signal = client?.signal
        ? AbortSignal.any([abortCtrl.signal, client.signal])
        : abortCtrl.signal;

      return runInInjectionContext(currentInjector, () =>
        tool.execute(args, {
          ...client,
          signal,
        }),
      );
    },
  };

  // Unregister when the associated `Injector` is destroyed.
  destroyRef.onDestroy(() => void abortCtrl.abort());

  await modelContext.registerTool(wrappedTool, {signal: abortCtrl.signal});
}