1. Optimised MongoDB query performance to achieve substantial reduction in response time for large datasets, containing millions of documents.2. Written robust unit tests using Mocha and Chai for Node.js applications, ensuring code quality and reliability.3. Tested software for bugs and operating speed, fixing bugs and documenting processes to increase efficiency.4. Optimized React.js components by removing unnecessary renders, ensured code reusability through decoupled components, resulting in cleaner and more maintainable code.