ipc: add .on

gluon.d.ts

@@ -179,7 +179,19 @@ type CDPApi = {
      * @default true
      */
     useSessionId?: boolean
-  ): Promise<any>
+  ): Promise<any>,
+
+  /**
+   * Hook into a specific CDP method being called.
+   * @returns Function to unhook/unsubscribe.
+   */
+  on(
+    /** Method of CDP command to hook into. */
+    method: string,
+
+    /** Callback to run when the given method is emitted. */
+    callback: (message: any) => void
+  ): (() => void)
 };
 
 type IdleAutoOptions = {

src/launcher/inject.js

@@ -109,7 +109,17 @@ export default async (CDP, proc, injectionType = 'browser', { dataPath, browserN
     ipc: IPC,
 
     cdp: {
-      send: (method, params, useSessionId = true) => CDP.sendMessage(method, params, useSessionId ? sessionId : undefined)
+      send: (method, params, useSessionId = true) => CDP.sendMessage(method, params, useSessionId ? sessionId : undefined),
+      on: (method, handler, once = false) => {
+        const unhook = CDP.onMessage(msg => {
+          if (msg.method === method) {
+            handler(msg);
+            if (once) unhook();
+          }
+        });
+
+        return unhook;
+      }
     },
 
     close: () => {