Adversarial JavaScript is everywhere - web pages, mobile apps, browser extensions… you name it! To better support the detection of adversarial JavaScript, Google is using MLIR to develop JSIR, a JavaScript intermediate representation. JSIR needs to support dataflow analysis to extract suspicious signals from the code, source-to-source transformations to simplify obfuscated code, and even binary-to-source transformations for bytecode decompilation. In this talk, we describe several IR design choices we made due to the unique requirements of adversarial code analysis.