Fix broken tests when module is not defined

diff --git a/src/dygraph.js b/src/dygraph.js
index 1e4d2dd..878a747 100644 (file)
--- a/src/dygraph.js
+++ b/src/dygraph.js
@@ -3747,7 +3747,7 @@ Dygraph.addAnnotationRule = function() {
   console.warn("Unable to add default annotation CSS rule; display may be off.");
 };
 
-if (module && module.exports) {
+if (typeof exports === "object" && typeof module !== "undefined") {
   module.exports = Dygraph;
 }