diff --git a/src/base/extStore.js b/src/base/extStore.js
index 539a468..e7d24c2 100644
--- a/src/base/extStore.js
+++ b/src/base/extStore.js
@@ -522,12 +522,13 @@ class SStoreDefinition {
  */
 function resolveOverwrite(key, container, overwriteBehaviour) {
     let dealAsMap = container instanceof Map;
-    let occurances = (dealAsMap
-        ? container.keys
-        : Object.keys(container)
+    let occurances = [...(
+        dealAsMap
+            ? container.keys()
+            : Object.keys(container)
     )
-        .filter(e => e.includes(key))
-        .length;
+        .filter(e => e.includes(key)
+        )].length;
 
     switch (overwriteBehaviour) {
         case OverwriteBehaviour.REPLACE:
diff --git a/src/context/scriptAndStyleContext.js b/src/context/scriptAndStyleContext.js
index 87c4956..bc9f137 100644
--- a/src/context/scriptAndStyleContext.js
+++ b/src/context/scriptAndStyleContext.js
@@ -50,8 +50,7 @@ class ScriptAndStyleContext {
         ].find(e => e !== '');
 
         /* deal with name already present */
-        let functionNames = this.#functions.keys;
-        if (functionNames.includes(registrationName)) {
+        if (this.#functions.has(registrationName)) {
             registrationName = resolveOverwrite(registrationName, this.#functions, overwriteBehaviour);
         }