Jalangi is an open source dynamic analysis framework for both front-end and back-end JavaScript. It allows you to monitor every operation of a JavaScript program and write your own program analysis code.

Jalangi Firefox extension intercepts and transforms every piece of JavaScript code in the webpage and external files. The code transformation adds hooks that allows you to monitor almost every operation (e.g., variable read/write, unary/binary operation, function/method call, etc.) performed by the execution. Simply overriding the API exposed allows you to perform your own dynamic analysis. Your dynamic analysis code will be executed side-by-side with the target program's execution.