perf: use faster check for $$ prefix

Use two calls to charAt instead of substr to detect a $$prefix in the shallowCopy functions.
This makes shallowCopy 25-50% faster (depending on which browser is used).
http://jsperf.com/angular-shallow-copy

Closes #5457

1 files changed, 1 insertions, 1 deletions

diff --git a/src/ngResource/resource.js b/src/ngResource/resource.js
index 281dd4ac..a007c7b1 100644
--- a/src/ngResource/resource.js
+++ b/src/ngResource/resource.js
@@ -35,7 +35,7 @@ function shallowClearAndCopy(src, dst) {
   });
 
   for (var key in src) {
-    if (src.hasOwnProperty(key) && key.substr(0, 2) !== '$$') {
+    if (src.hasOwnProperty(key) && key.charAt(0) !== '$' && key.charAt(1) !== '$') {
       dst[key] = src[key];
     }
   }