What are the main disadvantages of using Vanilla JS?

Vanilla JS's main disadvantage is that it has no built-in state management, component system, or virtual DOM, the way React or Vue do.

In practice, that means a team has to build and enforce its own conventions for connecting data to the DOM. Toggling a class when a value changes, keeping a counter displayed in three places in sync, or reacting to a form input all require writing the update logic by hand instead of declaring it once and letting a framework re-render automatically. On a small page this is barely noticeable. On a page with dozens of interactive elements, the same synchronization logic gets rewritten slightly differently in each place, and without a shared pattern the codebase drifts toward inconsistency as more people touch it.

The pain shows up most concretely in two places. First, state synchronization: when one piece of data drives multiple parts of the UI, vanilla code needs explicit calls to update each one, and it's easy to miss a spot when a new UI element is added later. Second, memory management: event listeners attached to DOM nodes have to be removed manually when those nodes are destroyed, or the removed elements stay referenced in memory and listeners keep firing on nodes no longer in the page. Frameworks handle both through their reactivity systems and component lifecycle hooks; vanilla JS leaves both to the developer.

These tradeoffs are manageable in small or well-bounded projects with a handful of interactive widgets, and mitigations exist: a light pub/sub or observable pattern for state, native Web Components for a form of structure, or a small utility library instead of a full framework. The tradeoff gets harder to justify once a project has many interdependent UI states and more than one or two developers touching the same code, since nothing enforces how those pieces are wired together.