fix(respondable): Avoid message duplication with messageId (#2816)

* refactor: rewrite respondable

* fix: use nodejs crypto for uuid.v4

* test(cmd): allow require('crypto')

lib/core/public/load.js

@@ -1,6 +1,7 @@
 import Audit from '../base/audit';
 import cleanup from './cleanup';
 import runRules from './run-rules';
+import respondable from '../utils/respondable';
 
 function runCommand(data, keepalive, callback) {
   var resolve = callback;
@@ -43,20 +44,21 @@ function runCommand(data, keepalive, callback) {
   }
 }
 
+if (window.top !== window) {
+  respondable.subscribe('axe.start', runCommand);
+  respondable.subscribe('axe.ping', (data, keepalive, respond) => {
+    respond({
+      axe: true
+    });
+  });
+}
+
 /**
  * Sets up Rules, Messages and default options for Checks, must be invoked before attempting analysis
  * @param  {Object} audit The "audit specification" object
  * @private
  */
 function load(audit) {
-  axe.utils.respondable.subscribe('axe.ping', (data, keepalive, respond) => {
-    respond({
-      axe: true
-    });
-  });
-
-  axe.utils.respondable.subscribe('axe.start', runCommand);
-
   axe._audit = new Audit(audit);
 }
 

lib/core/utils/index.js

@@ -74,5 +74,6 @@ export { default as setScrollState } from './set-scroll-state';
 export { default as toArray } from './to-array';
 export { default as tokenList } from './token-list';
 export { default as uniqueArray } from './unique-array';
+export { default as uuid } from './uuid';
 export { default as validInputTypes } from './valid-input-type';
 export { default as isValidLang, validLangs } from './valid-langs';