refactor(filterFilter): introduce helper function for "DRYness"

Author: gkalpak

src/ng/filter/filter.js

@@ -135,7 +135,7 @@ function filterFilter() {
       }
     }
 
-    var expressionType = (expression !== null) ? typeof expression : 'null';
+    var expressionType = getTypeForFilter(expression);
     var predicateFn;
     var matchAgainstAnyProp;
 
@@ -204,8 +204,8 @@ function createPredicateFn(expression, comparator, matchAgainstAnyProp) {
 }
 
 function deepCompare(actual, expected, comparator, matchAgainstAnyProp, dontMatchWholeObject) {
-  var actualType = (actual !== null) ? typeof actual : 'null';
-  var expectedType = (expected !== null) ? typeof expected : 'null';
+  var actualType = getTypeForFilter(actual);
+  var expectedType = getTypeForFilter(expected);
 
   if ((expectedType === 'string') && (expected.charAt(0) === '!')) {
     return !deepCompare(actual, expected.substring(1), comparator, matchAgainstAnyProp);
@@ -251,3 +251,8 @@ function deepCompare(actual, expected, comparator, matchAgainstAnyProp, dontMatc
       return comparator(actual, expected);
   }
 }
+
+// Used for easily differentiating between `null` and actual `object`
+function getTypeForFilter(val) {
+  return (val === null) ? 'null' : typeof val;
+}