Isomorphic JavaScript applications can share the same code and run on both the front end and back end. It is also a spectrum containing applications that share minimal bits of validation logic with ones that share a bulk of the application code. Nashorn is a new JavaScript engine for Java that was released with Java 8. The Nashorn JavaScript engine makes isomorphic web apps on the JVM possible by allowing the exact same browser code to run on the server. This enables us to achieve the don’t-repeat-yourself (DRY) principle, by reducing repetition in a multitier architecture. This presentation covers the key concepts, rationale, and categories of Isomorphic JavaScript and how it makes your large applications maintainable.