JavaScript injection is inserting unwanted JavaScript into Web pages with the intent on violating the security and privacy standards of the Web pages. There are a number of techniques that have been developed for the detection and prevention of JavaScript injection, and all have performance costs. While the performance issues of the JavaScript injection detection techniques have been mainly studied in running systems, we propose a simulation approach using UML SPT and JavaSim. The new approach not only reduces the cost for such analysis but also provides a framework for modeling injection detection techniques and analyzing the performance implications of design decisions.