fix(ngClass): ensure that ngClass only adds/removes the changed classes

ngClass works by removing all the former classes and then adding all the
new classes to the element during each watch change operation. This may
cause transition animations to never render. The ngClass directive will
now only add and remove the classes that change during each watch operation.

Closes #4960
Closes #4944

1 files changed, 23 insertions, 1 deletions

diff --git a/src/Angular.js b/src/Angular.js
index 8409f971..b27f4b06 100644
--- a/src/Angular.js
+++ b/src/Angular.js
@@ -80,7 +80,8 @@
     -assertArgFn,
     -assertNotHasOwnProperty,
     -getter,
-    -getBlockElements
+    -getBlockElements,
+    -tokenDifference
 
 */
 
@@ -1350,3 +1351,24 @@ function getBlockElements(block) {
 
   return jqLite(elements);
 }
+
+/**
+ * Return the string difference between tokens of the original string compared to the old string
+ * @param {str1} string original string value
+ * @param {str2} string new string value
+ */
+function tokenDifference(str1, str2) {
+  var values = '',
+      tokens1 = str1.split(/\s+/),
+      tokens2 = str2.split(/\s+/);
+
+  outer:
+  for(var i=0;i<tokens1.length;i++) {
+    var token = tokens1[i];
+    for(var j=0;j<tokens2.length;j++) {
+      if(token == tokens2[j]) continue outer;
+    }
+    values += (values.length > 0 ? ' ' : '') + token;
+  }
+  return values;
+}