As a React developer, there are several key skills that are essential for success in developing applications using the React framework. Here are some of the key skills:
- React.js: A deep understanding of React.js is crucial. This includes knowledge of React components, state management, lifecycle methods, and hooks.
- JavaScript: Since React is built with JavaScript, a strong foundation in JavaScript is essential. You should have a good grasp of core JavaScript concepts like variables, functions, loops, arrays, objects, and understanding of modern JavaScript features like arrow functions, async/await, and Promises.
- HTML/CSS: Proficiency in HTML and CSS is necessary to create the structure and style the user interface of React applications.
- JSX: JSX is an extension to JavaScript used in React for defining components. Familiarity with JSX syntax and how to use it effectively is important.
- Component-based architecture: Understanding how to design and build reusable components is key to developing scalable React applications. You should be able to break down UI elements into smaller, manageable components.
- State management: React provides local state management, but for more complex applications, you may need to work with state management libraries like Redux or MobX. Knowledge of these libraries and their integration with React is beneficial.
- React Router: React Router is a widely used library for handling routing in React applications. Understanding how to set up routes and navigate between different pages or views is important.
- API Integration: React applications often interact with APIs to fetch and send data. Knowledge of working with RESTful APIs or GraphQL, handling asynchronous operations with promises or async/await, and using fetch or Axios for data retrieval is necessary.
- Debugging and Testing: Proficiency in debugging React applications using browser developer tools and other debugging tools is important. Knowledge of testing frameworks like Jest or Enzyme for unit testing React components is also beneficial.
- Version Control: Familiarity with version control systems like Git and understanding concepts like branching, merging, and pull requests is important for collaborative development.
- Responsive Design: With the increasing usage of mobile devices, knowing how to create responsive and mobile-friendly UIs using CSS and media queries is valuable.
- Performance Optimization: Understanding techniques for optimizing React application performance, such as virtualization, code splitting, lazy loading, and minimizing re-renders, can greatly enhance the user experience.

My opinion is that a front-end developer should first of all demonstrate excellent knowledge of javascript, regardless of the framework. And of course, you need to deeply understand the eco-system of the framework you are working on.