DETECTING ERRORS IN WEB APPLICATION RUNTIME ENVIRONMENTS

Systems, methods, and computer program products to perform an operation comprising receiving a user action script, a first callback queue, and an asynchronous operation queue generated based on a first execution instance of a web application, simulating the first execution instance of the web application, comprising: invoking a second execution instance of the web application, simulating each user action of a plurality of user actions specified in the user action script, based on a plurality of callback functions specified in the first callback queue, simulating each asynchronous operation of a plurality of asynchronous operations specified in the asynchronous operation queue based on the plurality of callback functions specified in the first callback queue, and generating a second callback queue based on the simulated plurality of user actions and asynchronous operations.