Isomorphic js allows sharing of JavaScript code between a Drupal backend and React frontend. It enables component re-use, rapid development, and handling large codebases. Some benefits include self-contained and reusable components, sharing code between server and client, and using a virtual DOM for efficient UI updates. Challenges include getting data from Drupal to React and issues like overfetching or underfetching data. Solutions involve Flux data stores, GraphQL, and server-side rendering. Isomorphic JavaScript focuses developers on components, enables rapid prototyping, and treats frontend and backend as part of the same application.