Require a type for SkyElement attributes.

sky/framework/sky-element/sky-element.sky

 <!--
 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 -->
 <import src="sky-binder.sky" as="binder" />
 <script>
 var attributeConverters = {
   boolean: function(value) {
     if (typeof value == 'string')
       return value == 'true';
     return !!value;
   },
   number: function(value) {
     return Number(value);
   },
   string: function(value) {
     if (value === null)
       return '';
     return String(value);
   },
 };
 
 function parseAttributeSpec(spec) {
   var attributes = new Map();
-  var attributeTokens = (spec || '').split(',');
+
+  if (!spec)
+    return attributes;
+
+  var attributeTokens = spec.split(',');
 
   for (var i = 0; i < attributeTokens.length; ++i) {
     var parts = attributeTokens[i].split(':');
+
+    if (parts.length != 2) {
+      console.error('Invalid attribute spec "' + spec + '", attributes must' +
+          ' be {name}:{type}, where type is one of  boolean, number or' +
+          ' string.');
+      continue;
+    }
+
     var name = parts[0].trim();
-    var type = (parts[1] || '').trim();
-    var converter = attributeConverters[type] || attributeConverters.string;
+    var type = parts[1].trim();
+    var converter = attributeConverters[type];
+
+    if (!converter) {
+      console.error('Invalid attribute spec "' + spec + '", type must be one'
+          + ' of boolean, number or string.');
+      continue;
+    }
 
     attributes.set(name, converter);
   }
 
   return attributes;
 }
 
 function collectEventHandlers(definition) {
   var eventHandlers = [];
   var attributes = definition.getAttributes();
@@ skipping 198 matching lines @@
         binding.setValue(this[name]);
         binding.discardChanges();
       }
     }
     this.dirtyPropertyBindings = null;
   }
 };
 
 module.exports = SkyElement;
 </script>