run scripts on background page after onLoad

background/main.ts

@@ -22,20 +22,21 @@
 
 "use strict";
 
+window.addEventListener("load", () => {
+
   // TypeScript does not allow ".js" extensions in the
   // module name, so SystemJS must add it.
   System.config({
                  defaultJSExtensions: true,
                 });
 
-
   System.import("../lib/wallet/wxMessaging")
     .then((wxMessaging) => {
       // Export as global for debugger
       (window as any).wxMessaging = wxMessaging;
       wxMessaging.wxMain();
-      })
-      .catch((e) => {
+    }).catch((e) => {
       console.log("wallet failed");
       console.error(e.stack);
     });
+});