With the rapid development of mobile applications, it is important for every e-commerce app to find a balance between high performance and user-friendly design in order to make sure of a smooth and positive user experience. Developers today often face two main methods: native development, which offers strong performance and deep integration with the device, and cross-platform development, which allows faster deployment and easier maintenance through a shared codebase across multiple operating systems. This project intends to compare React Native, one of the most popular frameworks for cross-platform development, with Swift, the official language for native iOS development. The purpose of the study is to analyze which option provides better performance in terms of execution time, CPU usage, and RAM consumption. To perform this comparison, twelve applications will be developed, six in Swift and six in React Native. Each application built in Swift will have a similar version in React Native with the same functionality. Six different functions will be implemented, one in each app. For example, one of the Swift apps will include a filtering function, and its equivalent in React Native will have the same function. Performance will be analyzed by measuring execution time, CPU load, and memory usage. The study will also examine differences in how the frameworks manage device resources, as well as the user experience they deliver in practice. The goal of this research is to provide developers with practical understanding that can guide them in choosing the most relevant framework for their projects. This will be done by examining key functions such as writing, reading and updating data from databases, as well as analyzing how long it takes to fetch both large and small sets of data, together with other relevant aspects. The results showed that Swift generally performs better than React Native in terms of execution time, CPU usage, and RAM consumption, especially when handling larger data sets and features like filtering and CRUD operations. However, React Native showed better performance in for exemple state management, which may be an advantage for different types of applications. The choice of technology should be based on which features are most critical for the specific e-commerce application.