1 files changed, 28 insertions, 4 deletions

diff --git a/web/callback.js b/web/callback.js
index 1b3028e..178b8e9 100644
--- a/web/callback.js
+++ b/web/callback.js
@@ -2,20 +2,44 @@ addToLibrary({
 
 cbfl: [],
 
+validateCallbackId__deps: [ 'cbfl' ],
+validateCallbackId: function(i) {
+  if (i < 0) {
+    console.log("--- WARNING ---");
+    console.log("Trying to access callback function of invalid id " + i);
+    console.log("--- WARNING ---");
+    return false;
+  }
+
+  if (i >= _cbfl.length) {
+    console.log("--- WARNING ---");
+    console.log("Trying to access callback function " + i + ", but only "
+      + _cbfl.length + " have been registered. This may be caused by a "
+      + "call outside of the main thread.");
+    console.log("--- WARNING ---");
+    return false;
+  }
+
+  return true;
+},
+
 addCallbackFunction__deps: [ 'cbfl' ],
 addCallbackFunction: function(f) {
   _cbfl.push(f)
   return _cbfl.length - 1
 },
 
-callFunction__deps: [ 'cbfl' ],
+callFunction__deps: [ 'cbfl', 'validateCallbackId' ],
 callFunction: function(id, arg) {
-  _cbfl[id](UTF8ToString(arg))
+  if (_validateCallbackId(id))
+    _cbfl[id](UTF8ToString(arg));
 },
 
-callFunctionInt__deps: [ 'cbfl' ],
+callFunctionInt__deps: [ 'cbfl', 'validateCallbackId' ],
 callFunctionInt: function(id) {
-  return _cbfl[id]()
+  if (_validateCallbackId(id))
+    return _cbfl[id]();
+  return 0;
 },
 
 });