feat(context): add singleValue to ContextView

Author: raymondfeng

packages/context/src/__tests__/unit/context-view.unit.ts

@@ -45,6 +45,17 @@ describe('ContextView', () => {
     expect(await taggedAsFoo.asGetter()()).to.eql(['BAR', 'FOO']);
   });
 
+  it('reports error on singleValue() if multiple values exist', async () => {
+    return expect(taggedAsFoo.singleValue()).to.be.rejectedWith(
+      /The ContextView has more than one value\. Use values\(\) to access them\./,
+    );
+  });
+
+  it('supports singleValue() if only one value exist', async () => {
+    server.unbind('bar');
+    expect(await taggedAsFoo.singleValue()).to.eql('FOO');
+  });
+
   it('reloads bindings after refresh', async () => {
     taggedAsFoo.refresh();
     const abcBinding = server

packages/context/src/context-view.ts

@@ -157,6 +157,18 @@ export class ContextView<T = unknown> extends EventEmitter
   asGetter(session?: ResolutionSession): Getter<T[]> {
     return () => this.values(session);
   }
+
+  /**
+   * Get the single value
+   */
+  async singleValue(session?: ResolutionSession): Promise<T | undefined> {
+    const values = await this.values(session);
+    if (values.length === 0) return undefined;
+    if (values.length === 1) return values[0];
+    throw new Error(
+      'The ContextView has more than one value. Use values() to access them.',
+    );
+  }
 }
 
 /**