Which of the following is an example of a JavaScript framework?

React is a widely recognized JavaScript framework, primarily used for building user interfaces and front-end applications. It allows developers to create reusable UI components, making it easier to manage large-scale applications by breaking them down into smaller, manageable pieces. React employs a declarative style, enabling developers to describe what the UI should look like for any given state, and it handles the rendering of those changes efficiently.

The other options represent frameworks associated with different programming languages. Spring is a framework for building Java applications, Django is a framework for Python, and Ruby on Rails is associated with Ruby. While all these frameworks are influential in their respective environments, they are not related to JavaScript, which is essential for correctly identifying React as a JavaScript framework.