The virtual DOM is used for efficient re-rendering of the DOM. This isn't really related to dirty checking your data. You could re-render using a virtual DOM with or without dirty checking. With ReactJS, each time a change is triggered (by a query or a user’s action, for instance), the entire virtual DOM is updated. ReactJS keeps two versions of the virtual DOM in memory — an updated virtual DOM and a copy made before the update. After the update, ReactJS compares these two versions to find the elements that have changed. Then it updates only the part of the real DOM that has changed. There is some overhead in computing the diff between two virtual trees, but the virtual DOM diff is about understanding what needs updating in the DOM and not whether or not your data has changed.