perf($parse) use a faster path when the number of path parts is low

Use a faster path when the number of path tokens is low (ie the common case).
This results in a better than 19x improvement in the time spent in $parse and
produces output that is about the same speed in chrome and substantially faster
in firefox.
http://jsperf.com/angularjs-parse-getter/6

Closes #5359

Author: kseamon

src/ng/parse.js

@@ -891,19 +891,19 @@ function cspSafeGetterFn(key0, key1, key2, key3, key4, fullExp, options) {
       ? function cspSafeGetter(scope, locals) {
           var pathVal = (locals && locals.hasOwnProperty(key0)) ? locals : scope;
 
-          if (pathVal === null || pathVal === undefined) return pathVal;
+          if (pathVal == null) return pathVal;
           pathVal = pathVal[key0];
 
-          if (!key1 || pathVal === null || pathVal === undefined) return pathVal;
+          if (!key1 || pathVal == null) return pathVal;
           pathVal = pathVal[key1];
 
-          if (!key2 || pathVal === null || pathVal === undefined) return pathVal;
+          if (!key2 || pathVal == null) return pathVal;
           pathVal = pathVal[key2];
 
-          if (!key3 || pathVal === null || pathVal === undefined) return pathVal;
+          if (!key3 || pathVal == null) return pathVal;
           pathVal = pathVal[key3];
 
-          if (!key4 || pathVal === null || pathVal === undefined) return pathVal;
+          if (!key4 || pathVal == null) return pathVal;
           pathVal = pathVal[key4];
 
           return pathVal;
@@ -912,7 +912,7 @@ function cspSafeGetterFn(key0, key1, key2, key3, key4, fullExp, options) {
           var pathVal = (locals && locals.hasOwnProperty(key0)) ? locals : scope,
               promise;
 
-          if (pathVal === null || pathVal === undefined) return pathVal;
+          if (pathVal == null) return pathVal;
 
           pathVal = pathVal[key0];
           if (pathVal && pathVal.then) {
@@ -924,7 +924,7 @@ function cspSafeGetterFn(key0, key1, key2, key3, key4, fullExp, options) {
             }
             pathVal = pathVal.$$v;
           }
-          if (!key1 || pathVal === null || pathVal === undefined) return pathVal;
+          if (!key1 || pathVal == null) return pathVal;
 
           pathVal = pathVal[key1];
           if (pathVal && pathVal.then) {
@@ -936,7 +936,7 @@ function cspSafeGetterFn(key0, key1, key2, key3, key4, fullExp, options) {
             }
             pathVal = pathVal.$$v;
           }
-          if (!key2 || pathVal === null || pathVal === undefined) return pathVal;
+          if (!key2 || pathVal == null) return pathVal;
 
           pathVal = pathVal[key2];
           if (pathVal && pathVal.then) {
@@ -948,7 +948,7 @@ function cspSafeGetterFn(key0, key1, key2, key3, key4, fullExp, options) {
             }
             pathVal = pathVal.$$v;
           }
-          if (!key3 || pathVal === null || pathVal === undefined) return pathVal;
+          if (!key3 || pathVal == null) return pathVal;
 
           pathVal = pathVal[key3];
           if (pathVal && pathVal.then) {
@@ -960,7 +960,7 @@ function cspSafeGetterFn(key0, key1, key2, key3, key4, fullExp, options) {
             }
             pathVal = pathVal.$$v;
           }
-          if (!key4 || pathVal === null || pathVal === undefined) return pathVal;
+          if (!key4 || pathVal == null) return pathVal;
 
           pathVal = pathVal[key4];
           if (pathVal && pathVal.then) {
@@ -976,6 +976,27 @@ function cspSafeGetterFn(key0, key1, key2, key3, key4, fullExp, options) {
         };
 }
 
+function simpleGetterFn1(key0, fullExp) {
+  ensureSafeMemberName(key0, fullExp);
+
+  return function simpleGetterFn1(scope, locals) {
+    if (scope == null) return scope;
+    return ((locals && locals.hasOwnProperty(key0)) ? locals : scope)[key0];
+  };
+}
+
+function simpleGetterFn2(key0, key1, fullExp) {
+  ensureSafeMemberName(key0, fullExp);
+  ensureSafeMemberName(key1, fullExp);
+
+  return function simpleGetterFn2(scope, locals) {
+    if (scope == null) return scope;
+    scope = ((locals && locals.hasOwnProperty(key0)) ? locals : scope)[key0];
+
+    return scope == null ? scope : scope[key1];
+  };
+}
+
 function getterFn(path, options, fullExp) {
   // Check whether the cache has this getter already.
   // We can use hasOwnProperty directly on the cache because we ensure,
@@ -988,7 +1009,13 @@ function getterFn(path, options, fullExp) {
       pathKeysLength = pathKeys.length,
       fn;
 
-  if (options.csp) {
+  // When we have only 1 or 2 tokens, use optimized special case closures.
+  // http://jsperf.com/angularjs-parse-getter/6
+  if (!options.unwrapPromises && pathKeysLength === 1) {
+    fn = simpleGetterFn1(pathKeys[0], fullExp);
+  } else if (!options.unwrapPromises && pathKeysLength === 2) {
+    fn = simpleGetterFn2(pathKeys[0], pathKeys[1], fullExp);
+  } else if (options.csp) {
     if (pathKeysLength < 6) {
       fn = cspSafeGetterFn(pathKeys[0], pathKeys[1], pathKeys[2], pathKeys[3], pathKeys[4], fullExp,
                           options);
@@ -1006,11 +1033,10 @@ function getterFn(path, options, fullExp) {
       };
     }
   } else {
-    var code = 'var l, fn, p;\n';
+    var code = 'var p;\n';
     forEach(pathKeys, function(key, index) {
       ensureSafeMemberName(key, fullExp);
-      code += 'if(s === null || s === undefined) return s;\n' +
-              'l=s;\n' +
+      code += 'if(s == null) return s;\n' +
               's='+ (index
                       // we simply dereference 's' on any .dot notation
                       ? 's'
@@ -1033,10 +1059,10 @@ function getterFn(path, options, fullExp) {
     /* jshint -W054 */
     var evaledFnGetter = new Function('s', 'k', 'pw', code); // s=scope, k=locals, pw=promiseWarning
     /* jshint +W054 */
-    evaledFnGetter.toString = function() { return code; };
-    fn = function(scope, locals) {
+    evaledFnGetter.toString = valueFn(code);
+    fn = options.unwrapPromises ? function(scope, locals) {
       return evaledFnGetter(scope, locals, promiseWarning);
-    };
+    } : evaledFnGetter;
   }
 
   // Only cache the value if it's not going to mess up the cache object

test/ng/parseSpec.js

@@ -906,6 +906,7 @@ describe('parser', function() {
             expect($parse('a.b')({a: {b: 0}}, {a: {b:1}})).toEqual(1);
             expect($parse('a.b')({a: null}, {a: {b:1}})).toEqual(1);
             expect($parse('a.b')({a: {b: 0}}, {a: null})).toEqual(undefined);
+            expect($parse('a.b.c')({a: null}, {a: {b: {c: 1}}})).toEqual(1);
           }));
         });