React (also written React.js or ReactJS) is an open source JavaScript library created by Facebook (now Meta) and released in 2013, used to build user interfaces from reusable components. Each component manages its own state, and React updates the display automatically when that state changes.
Technically, it is not a full framework: React handles the view layer, and other tools are added for routing, data management or server-side rendering. Next.js is the most widely used framework for building complete applications on React. React Native applies the same principles to mobile apps.
It is one of the most widespread front-end technologies, from startups to large groups, which makes it a safe choice for hiring and maintaining a team.
Why it matters when hiring
React is so widespread that nearly every front-end resume lists it: the keyword does not filter anything. What sets a strong profile apart is mastery of state and rendering (when a component re-renders and why), architecture of a large codebase, and TypeScript. In interviews, have them explain a performance problem they solved. Note that React Native and React for the web are related but distinct skills.