A Light-Weight Effect System for JavaScript

While types describe what values an expression computes, the effects of an expression describe how it is computed, e.g. whether its evaluation manipulates global state, accesses the file system or may throw certain exceptions. Having to specify types and effects throughout the program might not be feasible in a scripting language but selective, sparse effect annotations may still help to prevent many programming errors. This paper described the design and implementation of a system that statically checks effects in otherwise dynamically-typed JavaScript programs.