Add script caching

worker.ts

@@ -1,4 +1,6 @@
 // isolator/worker.ts
+const moduleCache = new Map();
+
 const States = Object.freeze({
   SUCCESS: "SUCCESS",
   NOT_A_FUNCTION: "NOT_A_FUNCTION",
@@ -50,11 +52,15 @@ self.onmessage = async (e) => {
         status
       );
 
-    // Use a data URL to import the user's code as an ES module.
-    const dataUrl = `data:text/javascript;base64,${btoa(
-      unescape(encodeURIComponent(code))
-    )}`;
-    const userModule = await import(dataUrl);
+    let userModule = moduleCache.get(code);
+    if (!userModule) {
+      // Use a data URL to import the user's code as an ES module.
+      const dataUrl = `data:text/javascript;base64,${btoa(
+        unescape(encodeURIComponent(code))
+      )}`;
+      userModule = await import(dataUrl);
+      moduleCache.set(code, userModule);
+    }
 
     if (typeof userModule.default !== "function") {
       throw new Error(