Add _.where fast path for the common use case or passing an object with one property.

Former-commit-id: dfb78f59ae22f3ccdd88d58cefdb8abcde58eda6

build.js

@@ -102,7 +102,7 @@
     'compose': [],
     'contains': ['basicEach', 'getIndexOf', 'isString'],
     'countBy': ['createCallback', 'forEach'],
-    'createCallback': ['identity', 'isEqual', 'keys'],
+    'createCallback': ['identity', 'isEqual', 'isObject', 'keys'],
     'debounce': ['isObject'],
     'defaults': ['createCallback', 'createIterator'],
     'defer': ['bind'],
@@ -3657,6 +3657,15 @@
             '    : (first ? find : filter)(collection, properties);',
             '}'
           ].join('\n'));
+
+          // simplify `_.createCallback`
+          source = source.replace(matchFunction(source, 'createCallback'), function(match) {
+            return match
+              // remove unnecessary fast path
+              .replace(/^(( *)var props *=.+?),[\s\S]+?\n\2}/m, '$1;')
+              // remove `_.isEqual` use
+              .replace(/=.+?\bisEqual\((.+?), *(.+?),.+?\)/, '= $1 === $2');
+          });
         }
         // replace `_.zip`
         if(!isLodash('zip')) {
@@ -3703,12 +3712,6 @@
           }
         });
 
-        // remove `_.isEqual` use from `createCallback`
-        if (!isLodash('where')) {
-          source = source.replace(matchFunction(source, 'createCallback'), function(match) {
-            return match.replace(/=.+?\bisEqual\((.+?), *(.+?),.+?\)/, '= $1 === $2');
-          });
-        }
         // remove unused features from `createBound`
         if (_.every(['bindKey', 'partial', 'partialRight'], function(funcName) {
               return !_.contains(buildFuncs, funcName);

lodash.js

@@ -4762,10 +4762,20 @@
             return object[func];
           };
         }
-        var props = keys(func);
+        var props = keys(func),
+            key = props[0],
+            a = func[key];
+
+        if (props.length == 1 && a === a && !isObject(a)) {
+          return function(object) {
+            var b = object[key];
+            return a === b && (a !== 0 || (1 / a == 1 / b));
+          };
+        }
         return function(object) {
           var length = props.length,
               result = false;
+
           while (length--) {
             if (!(result = isEqual(object[props[length]], func[props[length]], indicatorObject))) {
               break;