Add JSON-RPC 2.0 notification support to client

src/sidebar/util/postmessage-json-rpc.js

@@ -98,3 +98,21 @@ export function call(
       throw err;
     });
 }
+
+/**
+ * Send a JSON-RPC 2.0 notification request to another frame via `postMessage`.
+ * No response is expected.
+ *
+ * @param {Window} frame - Frame to send call to
+ * @param {string} origin - Origin filter for `window.postMessage` call
+ * @param {string} method - Name of the JSON-RPC method
+ * @param {unknown[]} params - Parameters of the JSON-RPC method
+ */
+export function notify(frame, origin, method, params = []) {
+  const request = {
+    jsonrpc: '2.0',
+    method,
+    params,
+  };
+  frame.postMessage(request, origin);
+}

src/sidebar/util/test/postmessage-json-rpc-test.js

 import EventEmitter from 'tiny-emitter';
 
-import { call, $imports } from '../postmessage-json-rpc';
+import { call, notify, $imports } from '../postmessage-json-rpc';
 
 class FakeWindow {
   constructor() {
@@ -14,6 +14,25 @@ describe('sidebar/util/postmessage-json-rpc', () => {
   const origin = 'https://embedder.com';
   const messageId = 42;
 
+  describe('notify', () => {
+    let frame;
+
+    beforeEach(() => {
+      frame = { postMessage: sinon.stub() };
+    });
+
+    it('should send a JSON-RPC 2.0 notification to the frame', () => {
+      notify(frame, origin, 'testMethod', [1, 2, 3]);
+
+      assert.calledOnce(frame.postMessage);
+      assert.calledWith(frame.postMessage, {
+        jsonrpc: '2.0',
+        method: 'testMethod',
+        params: [1, 2, 3],
+      });
+    });
+  });
+
   describe('call', () => {
     let frame;
     let fakeWindow;