From 94afd58b2f97960cac1004f3a8be2681e8e1adac Mon Sep 17 00:00:00 2001
From: Paul Kaplan <pkaplan@media.mit.edu>
Date: Fri, 31 May 2019 08:35:27 -0400
Subject: [PATCH] Require handleMessage to be set before opening
 scratch-link-socket

---
 src/util/scratch-link-websocket.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/util/scratch-link-websocket.js b/src/util/scratch-link-websocket.js
index 8eb4c13dc..8c8a2becf 100644
--- a/src/util/scratch-link-websocket.js
+++ b/src/util/scratch-link-websocket.js
@@ -33,12 +33,12 @@ class ScratchLinkWebSocket {
             throw new Error(`Unknown ScratchLink socket Type: ${this._type}`);
         }
 
-        if (this._onOpen && this._onClose && this._onError) {
+        if (this._onOpen && this._onClose && this._onError && this._handleMessage) {
             this._ws.onopen = this._onOpen;
             this._ws.onclose = this._onClose;
             this._ws.onerror = this._onError;
         } else {
-            throw new Error('Must set open, close and error handlers before calling open on the socket');
+            throw new Error('Must set open, close, message and error handlers before calling open on the socket');
         }
 
         this._ws.onmessage = this._onMessage.bind(this);