The goal of this analysis is to gather information about the types of variables and object fields in JavaScript programs so that they can be better optimized. More specifically, the analysis should allow a JavaScript compiler to obtain some guarantees about the behavior of programs to compile, allowing it to generate more specialized code. When compiling JavaScript code, a naive JavaScript compiler has to assume that the + operator can be either addition or string concatenation, and produce code that can handle both cases, with the associated dynamic dispatch overhead.