fix: make the primary domain communicator a singleton per cypress instance

Author: AtofStryker

packages/driver/src/multi-domain/communicator.ts

@@ -6,6 +6,7 @@ import { preprocessForSerialization, reifyCrossDomainError } from '../util/seria
 const debug = debugFn('cypress:driver:multi-domain')
 
 const CROSS_DOMAIN_PREFIX = 'cross:domain:'
+let primaryDomainCommunicatorSingleton: PrimaryDomainCommunicator | null = null
 
 /**
  * Primary domain communicator. Responsible for sending/receiving events throughout
@@ -23,6 +24,24 @@ export class PrimaryDomainCommunicator extends EventEmitter {
   private crossDomainDriverWindows: {[key: string]: Window} = {}
   userInvocationStack?: string
 
+  constructor () {
+    // There should only be one PrimaryDomainCommunicator per Cypress instance (Ex: primary domain, specbridge1, specbridge2, ...).
+    // Spec Bridges will create a PrimaryDomainCommunicator instance, but will never initialize the window.top message listener
+    // this means that methods that communicate through postMessage can send, but spec bridge PrimaryDomainCommunicator
+    // will never receive any events.
+    if (!primaryDomainCommunicatorSingleton) {
+      // @ts-ignore
+      super()
+      primaryDomainCommunicatorSingleton = this
+    }
+
+    // for the primary domain, the PrimaryDomainCommunicator needs to be a singleton.
+    // multiple PrimaryDomainCommunicator instances recreated on test refreshes/reloads cause dangling instances
+    // of the window.top message listener, stacking message events multiple times.
+    // The window.top instance does not change between test reloads, and we only need to bind it once
+    return primaryDomainCommunicatorSingleton
+  }
+
   /**
    * Initializes the event handler to receive messages from the spec bridge.
    * @param {Window} win - a reference to the window object in the primary domain.