update castArray implementation to use Array.from, etc

Signed-off-by: Christopher Hiller <boneskull@boneskull.com>

lib/utils.js

@@ -650,16 +650,25 @@ exports.isBrowser = function isBrowser() {
  * Casts `value` to an array; useful for optionally accepting array parameters
  *
  * It follows these rules, depending on `value`.  If `value` is...
- * 1. An `Array`: return a copy
- * 2. An `arguments` object: coerce to a proper Array and return it
- * 3. Any _defined_ value: return a new Array containing the single value
- * 4. `undefined`, return an empty Array
+ * 1. `undefined`: return an empty Array
+ * 2. `null`: return an array with a single `null` element
+ * 3. Any other object: return the value of `Array.from()` _if_ the object is iterable
+ * 4. otherwise: return an array with a single element, `value`
  * @param {*} value - Something to cast to an Array
  * @returns {*[]}
  */
 exports.castArray = function castArray(value) {
-  if (Array.isArray(value) || type(value) === 'arguments') {
-    return Array.prototype.slice.call(value);
+  if (value === undefined) {
+    return [];
+  }
+  if (value === null) {
+    return [null];
+  }
+  if (
+    typeof value === 'object' &&
+    typeof value[Symbol.iterator] === 'function'
+  ) {
+    return Array.from(value);
   }
-  return typeof value !== 'undefined' ? [value] : [];
+  return [value];
 };

test/unit/utils.spec.js

@@ -784,5 +784,11 @@ describe('lib/utils', function() {
         expect(utils.castArray('butts'), 'to equal', ['butts']);
       });
     });
+
+    describe('when provided null', function() {
+      it('should return an array containing a null value only', function() {
+        expect(utils.castArray(null), 'to equal', [null]);
+      });
+    });
   });
 });