[MessageHandler] Convert the code to a proper class

src/shared/message_handler.js

@@ -61,7 +61,8 @@ function wrapReason(reason) {
   }
 }
 
-function MessageHandler(sourceName, targetName, comObj) {
+class MessageHandler {
+  constructor(sourceName, targetName, comObj) {
     this.sourceName = sourceName;
     this.targetName = targetName;
     this.comObj = comObj;
@@ -134,9 +135,8 @@ function MessageHandler(sourceName, targetName, comObj) {
       action(data.data);
     };
     comObj.addEventListener('message', this._onComObjOnMessage);
-}
+  }
 
-MessageHandler.prototype = {
   on(actionName, handler) {
     if (typeof PDFJSDev === 'undefined' ||
         PDFJSDev.test('!PRODUCTION || TESTING')) {
@@ -148,7 +148,8 @@ MessageHandler.prototype = {
       throw new Error(`There is already an actionName called "${actionName}"`);
     }
     ah[actionName] = handler;
-  },
+  }
+
   /**
    * Sends a message to the comObj to invoke the action with the supplied data.
    * @param {string} actionName - Action to call.
@@ -156,13 +157,14 @@ MessageHandler.prototype = {
    * @param {Array} [transfers] - List of transfers/ArrayBuffers.
    */
   send(actionName, data, transfers) {
-    this.postMessage({
+    this._postMessage({
       sourceName: this.sourceName,
       targetName: this.targetName,
       action: actionName,
       data,
     }, transfers);
-  },
+  }
+
   /**
    * Sends a message to the comObj to invoke the action with the supplied data.
    * Expects that the other side will callback with the response.
@@ -176,7 +178,7 @@ MessageHandler.prototype = {
     const capability = createPromiseCapability();
     this.callbackCapabilities[callbackId] = capability;
     try {
-      this.postMessage({
+      this._postMessage({
         sourceName: this.sourceName,
         targetName: this.targetName,
         action: actionName,
@@ -187,7 +189,8 @@ MessageHandler.prototype = {
       capability.reject(ex);
     }
     return capability.promise;
-  },
+  }
+
   /**
    * Sends a message to the comObj to invoke the action with the supplied data.
    * Expect that the other side will callback to signal 'start_complete'.
@@ -214,7 +217,7 @@ MessageHandler.prototype = {
           cancelCall: null,
           isClosed: false,
         };
-        this.postMessage({
+        this._postMessage({
           sourceName,
           targetName,
           action: actionName,
@@ -257,8 +260,11 @@ MessageHandler.prototype = {
         return cancelCapability.promise;
       },
     }, queueingStrategy);
-  },
+  }
 
+  /**
+   * @private
+   */
   _createStreamSink(data) {
     const self = this;
     const action = this.actionHandler[data.action];
@@ -281,7 +287,7 @@ MessageHandler.prototype = {
           this.sinkCapability = createPromiseCapability();
           this.ready = this.sinkCapability.promise;
         }
-        self.postMessage({
+        self._postMessage({
           sourceName,
           targetName,
           stream: StreamKind.ENQUEUE,
@@ -349,8 +355,11 @@ MessageHandler.prototype = {
         reason: wrapReason(reason),
       });
     });
-  },
+  }
 
+  /**
+   * @private
+   */
   _processStreamMessage(data) {
     const streamId = data.streamId;
     const sourceName = this.sourceName;
@@ -482,8 +491,11 @@ MessageHandler.prototype = {
       default:
         throw new Error('Unexpected stream case');
     }
-  },
+  }
 
+  /**
+   * @private
+   */
   async _deleteStreamController(streamId) {
     // Delete the `streamController` only when the start, pull, and cancel
     // capabilities have settled, to prevent `TypeError`s.
@@ -495,26 +507,26 @@ MessageHandler.prototype = {
       return capability && capability.promise.catch(function() { });
     }));
     delete this.streamControllers[streamId];
-  },
+  }
 
   /**
    * Sends raw message to the comObj.
-   * @private
    * @param {Object} message - Raw message.
    * @param transfers List of transfers/ArrayBuffers, or undefined.
+   * @private
    */
-  postMessage(message, transfers) {
+  _postMessage(message, transfers) {
     if (transfers && this.postMessageTransfers) {
       this.comObj.postMessage(message, transfers);
     } else {
       this.comObj.postMessage(message);
     }
-  },
+  }
 
   destroy() {
     this.comObj.removeEventListener('message', this._onComObjOnMessage);
-  },
-};
+  }
+}
 
 export {
   MessageHandler,