JavaScript is used in various areas recently and is ongoing study now. Furthermore, there is a lot of potential for growth. We have been studying JavaScript in various aspects and developing a tool, namely Scalable Analysis Framework for ECMAScript (SAFE.) While several modules exist in SAFE, in this paper, we concentrate on the bug detector module and explain how we implemented the module and how we extended the module to detect more bugs. Additionally, we also extended the single-thread analysis to the multi-thread one to reduce analysis time and we implemented a new worklist order algorithm to maximize basic block coverage within the given number of iterations. The new worklist order algorithm also reduces the analysis time. For each methods, the multi-thread analysis has reduced analysis time up to 74.8% and the new worklist order algorithm has reduced analysis time up to 64.4%. We also have decreased analysis time up to 87.2% by combining two methods.