diff --git a/src/editor/sandbox/loopController.js b/src/editor/sandbox/loopController.js
index cceb952..012f11f 100644
--- a/src/editor/sandbox/loopController.js
+++ b/src/editor/sandbox/loopController.js
@@ -1,9 +1,9 @@
-const LoopController = {
-  _config: {
+const LoopController = Object.freeze({
+  _config: Object.freeze({
     maxExecTimePerLoop: 1e4,
     maxLoopCount: 1e6
-  },
-  loopMap: new Map(),
+  }),
+  _loopMap: new Map(),
   initLoop(loopID) {
     this.setLoop(loopID, {
       isInit: true,
@@ -13,22 +13,22 @@
     });
   },
   getLoop(loopID) {
-    return this.loopMap.get(loopID);
+    return this._loopMap.get(loopID);
   },
   setLoop(loopID, loop) {
-    this.loopMap.set(loopID, loop);
+    this._loopMap.set(loopID, loop);
   },
   delLoop(loopID) {
-    this.loopMap.delete(loopID);
+    this._loopMap.delete(loopID);
   },
   clearLoops() {
-    this.loopMap.clear();
+    this._loopMap.clear();
   },
   exitLoop(loopID) {
     this.delLoop(loopID);
   },
   calcLoop(loopID) {
-    if (this.loopMap.has(loopID)) {
+    if (this._loopMap.has(loopID)) {
       let { isInit, totalExecTime, startTime, count } = this.getLoop(loopID);
       if (isInit) {
         totalExecTime = Date.now() - startTime;
@@ -57,4 +57,4 @@
       );
     }
   }
-};
+});
diff --git a/src/editor/sandbox/setup.js b/src/editor/sandbox/setup.js
index 63480b2..56147bd 100644
--- a/src/editor/sandbox/setup.js
+++ b/src/editor/sandbox/setup.js
@@ -104,6 +104,12 @@
   });
   win.self = win.window = win.globalThis = win;
 
+  Object.defineProperty(document, 'defaultView', {
+    value: win,
+    writable: false,
+    configurable: false
+  });
+
   const api = {
     dispose() {
       if (chartInstance) {
diff --git a/src/editor/sandbox/srcdoc.html b/src/editor/sandbox/srcdoc.html
index b22b6f0..515fa6b 100644
--- a/src/editor/sandbox/srcdoc.html
+++ b/src/editor/sandbox/srcdoc.html
@@ -1,7 +1,9 @@
 <!DOCTYPE html>
 <html>
   <head>
+    <meta charset="utf-8" />
     <meta http-equiv="content-security-policy" content="__CSP__" />
+    <link rel="dns-prefetch" href="https://cdn.jsdelivr.net" />
     <style>
       * {
         margin: 0;