When running a piece of javascript code by using JSEvaluateScript() or JSObjectCallAsFunction(), the native code might be blocked because of dead loop or some other abnormal things in javascript code. In this case, a mechanism to let native code be able to interrupt the javascript code by throwing a javascript exception would be very useful. A simple solution would be: Provides an API to let C++ code register a callback to JavaScriptCore, then this callback will be called after certain number of javascript instructions have been executed. SpiderMonkey has similar feature, see: https://developer.mozilla.org/en/SpiderMonkey/JSAPI_Reference/JS_SetOperationCallback https://developer.mozilla.org/en/SpiderMonkey/JSAPI_Reference/JS_SetBranchCallback