Add has internal function

In some cases, `_.countby()` and `_.groupBy()`, we want to support
arrays as valid keys, since they can be coerced to strings. In the other
cases, the keys are known to always be strings anyway, so we can save
having to do the `_.isArray` check.

Fixes #2756.

Author: captbaritone

test/collections.js

@@ -758,6 +758,9 @@
       6: [jordan]
     };
     assert.deepEqual(_.groupBy(collection, ['stats', 'power']), expected, 'can group by deep properties');
+
+    var foos = [{foo: [1, 2]}, {foo: [1, 2]}]
+    assert.deepEqual(_.groupBy(foos, 'foo'), {"1,2": foos}, 'will coerce arrays to string keys');
   });
 
   QUnit.test('indexBy', function(assert) {
@@ -805,6 +808,9 @@
     grouped = _.countBy(array);
     assert.strictEqual(grouped['1'], 2);
     assert.strictEqual(grouped['3'], 1);
+
+    var foos = [{foo: [1, 2]}, {foo: [1, 2]}]
+    assert.deepEqual(_.countBy(foos, 'foo'), {'1,2': 2}, 'will coerce arrays to string keys');
   });
 
   QUnit.test('shuffle', function(assert) {

underscore.js

@@ -148,6 +148,10 @@
     };
   };
 
+  var has = function(obj, path) {
+    return obj != null && hasOwnProperty.call(obj, path);
+  }
+
   var deepGet = function(obj, path) {
     var length = path.length;
     for (var i = 0; i < length; i++) {
@@ -445,7 +449,7 @@
   // Groups the object's values by a criterion. Pass either a string attribute
   // to group by, or a function that returns the criterion.
   _.groupBy = group(function(result, value, key) {
-    if (_.has(result, key)) result[key].push(value); else result[key] = [value];
+    if (has(result, key)) result[key].push(value); else result[key] = [value];
   });
 
   // Indexes the object's values by a criterion, similar to `groupBy`, but for
@@ -458,7 +462,7 @@
   // either a string attribute to count by, or a function that returns the
   // criterion.
   _.countBy = group(function(result, value, key) {
-    if (_.has(result, key)) result[key]++; else result[key] = 1;
+    if (has(result, key)) result[key]++; else result[key] = 1;
   });
 
   var reStrSymbol = /[^\ud800-\udfff]|[\ud800-\udbff][\udc00-\udfff]|[\ud800-\udfff]/g;
@@ -811,7 +815,7 @@
     var memoize = function(key) {
       var cache = memoize.cache;
       var address = '' + (hasher ? hasher.apply(this, arguments) : key);
-      if (!_.has(cache, address)) cache[address] = func.apply(this, arguments);
+      if (!has(cache, address)) cache[address] = func.apply(this, arguments);
       return cache[address];
     };
     memoize.cache = {};
@@ -978,7 +982,7 @@
 
     // Constructor is a special case.
     var prop = 'constructor';
-    if (_.has(obj, prop) && !_.contains(keys, prop)) keys.push(prop);
+    if (has(obj, prop) && !_.contains(keys, prop)) keys.push(prop);
 
     while (nonEnumIdx--) {
       prop = nonEnumerableProps[nonEnumIdx];
@@ -994,7 +998,7 @@
     if (!_.isObject(obj)) return [];
     if (nativeKeys) return nativeKeys(obj);
     var keys = [];
-    for (var key in obj) if (_.has(obj, key)) keys.push(key);
+    for (var key in obj) if (has(obj, key)) keys.push(key);
     // Ahem, IE < 9.
     if (hasEnumBug) collectNonEnumProps(obj, keys);
     return keys;
@@ -1279,7 +1283,7 @@
       while (length--) {
         // Deep compare each member
         key = keys[length];
-        if (!(_.has(b, key) && eq(a[key], b[key], aStack, bStack))) return false;
+        if (!(has(b, key) && eq(a[key], b[key], aStack, bStack))) return false;
       }
     }
     // Remove the first object from the stack of traversed objects.
@@ -1329,7 +1333,7 @@
   // there isn't any inspectable "Arguments" type.
   if (!_.isArguments(arguments)) {
     _.isArguments = function(obj) {
-      return _.has(obj, 'callee');
+      return has(obj, 'callee');
     };
   }
 
@@ -1371,7 +1375,7 @@
   // on itself (in other words, not on a prototype).
   _.has = function(obj, path) {
     if (!_.isArray(path)) {
-      return obj != null && hasOwnProperty.call(obj, path);
+      return has(obj, path);
     }
     var length = path.length;
     for (var i = 0; i < length; i++) {