Don't show any circular reference errors when getDataElementValues is…

… called with a list of data elements that don't have circular references.

This fixes this issue:
adobe/reactor-extension-cloud-connector-edge#5.

src/__tests__/createGetDataElementValues.test.js

@@ -44,4 +44,17 @@ describe('function returned by createGetDataElementValues', () => {
       expect(getDataElementValue).toHaveBeenCalledWith('de1', context);
     });
   });
+
+  test('sends a cloned dataElementCallStack to getDataElementValue', () => {
+    const getDataElementValues = createGetDataElementValues(
+      (dataElementName, { dataElementCallStack }) => {
+        dataElementCallStack.push(dataElementName);
+
+        expect(dataElementCallStack).toStrictEqual([dataElementName]);
+      }
+    );
+
+    const context = {};
+    return getDataElementValues(['de1', 'de2'], context);
+  });
 });

src/createGetDataElementValues.js

@@ -9,10 +9,11 @@ OF ANY KIND, either express or implied. See the License for the specific languag
 governing permissions and limitations under the License.
 */
 
-module.exports = (getDataElementValue) => (tokenList, context) =>
-  Promise.all(
+module.exports = (getDataElementValue) => (tokenList, context) => {
+  const { dataElementCallStack = [] } = context;
+
+  return Promise.all(
     tokenList.map((t) => {
-      const { dataElementCallStack = [] } = context;
       context.dataElementCallStack = dataElementCallStack.slice();
 
       return getDataElementValue(t, context);
@@ -26,3 +27,4 @@ module.exports = (getDataElementValue) => (tokenList, context) =>
 
     return (name) => zipResults[name];
   });
+};