Andrei@Constantinescu.io
andrei@constantinescu.io

Summary

JavaScript Consultant with 10+ years of experience creating scalable web apps and intuitive interfaces using React, Next.js, and Node.js. I've developed microfrontend bridges for mobile apps, engineered a personal privacy-focused service network, and currently building a fitness app powered by React Native. When I'm not fine-tuning my custom LLM or at the gym, I'm delivering impactful solutions. Open to both short-term and long-term roles where I can make an immediate impact.

Skills

Highlights

contractCitibank UK(Financial)
React Front End Developer
Apr 2025 - Current
  • Engineered complete ag-Grid UI migration to latest version using React hooks and functional components, achieving 100% feature parity while improving grid rendering performance by 35% and enhancing UI responsiveness for large datasets (10,000+ rows) in trading positions and market data views.
  • Redesigned component architecture implementing React.memo, useMemo, and useCallback optimization patterns alongside RxJS observables for efficient real-time data rendering, resulting in smoother interactions, reduced UI lag, and faster updates across complex trading workflows.
  • Enhanced UI reliability through robust error boundaries, skeleton loading states, and optimistic UI updates, ensuring traders experience minimal friction and consistent interface behavior during data-intensive operations.
  • Maintained feature parity with legacy implementation while modernizing the codebase, ensuring seamless user experience for production traders.
contractUnlikelyAI(AI)
UI Developer
Apr 2024 - May 2024
  • Delivered front-end services for a chat-based application revamp, feature enhancements, and graph-based interface using React and Tailwind.
  • Implemented a new UI, prioritizing fast performance and intuitive usability, to deliver a seamless and engaging experience.
  • Contributed to an interactive graph-based interface, leveraging on React and canvas to create visually engaging data visualizations that effectively communicated complex information.
contractBalyasny Asset Management LLP(Financial)
UI Developer
Oct 2022 - Dec 2023
  • Orchestrated the creation and refinement of complex internal trading analysis tools using ReactJS, NextJS, GraphQL and Ag-grid, elevating our analytical prowess.
  • Optimized application efficiency by downsizing bundle size by 20% and enhanced user interaction speeds by 25% through strategic code optimizations and advanced caching techniques.
  • Facilitated consistent code and UI quality across projects by contributing to the development of a centralized monorepo, simplifying maintenance and updates.
contractCMC Markets plc(Trading)
software consultant
Jul 2021 - Sep 2022
  • Co-developed a ReactJS PWA investment app for internal customer support, enhancing digital customer engagement.
  • Engineered seamless user flow integration into mobile native apps through microfrontend architecture, improving cross-platform consistency.
  • Orchestrated native wkWebkitViews SwiftUI integrations, balancing native responsiveness with web robustness.
  • Elevated web performance within native apps by 30%, and reduced bundle size by 20% via strategic tree shaking and code splitting.
contractBP plc(Energy)
software consultant
Mar 2020 - Mar 2021
  • Architected a versatile framework-agnostic Payments SDK supporting diverse payment methods, powered by Typescript with a 90% unit test coverage via Jest.
  • Developed an internal sandbox app using ReactJS to validate various payment scenarios and ensure robust SDK functionality.
  • Implemented an AWS-based user login monitor, bolstering security with automated alerts and email notifications under specific conditions.
  • Contributed to an agile team environment, driving improvements and technical debt resolution through proactive collaboration and pair programming.
contractPartners Capital LLP(Financial)
frontend developer
Sep 2019 - Mar 2020
  • Engineered robust frontend features for a digital transformation project, converting Excel-based processes to a ReactJS and Typescript driven application.
  • Optimized application responsiveness by 35% with strategic memoization techniques and state normalization, significantly enhancing user interaction.
  • Advocated for and executed a comprehensive end-to-end testing regime using Cypress, bolstering feature reliability and system integrity.
contractKaluza(Energy)
senior frontend developer
Jun 2019 - Sep 2019
  • Pioneered the development of a real-time dashboard for smart device analytics, integrating with NodeJS and Kafka streams for live data feeds.
  • Customized UK map visualizations using GeoJSON and WebGL, and employed D3.js for dynamic data representation.
  • Curated a Storybook component library to streamline collaboration between design and development teams, enhancing UI consistency and development efficiency.
  • Mentored junior team members, facilitating knowledge transfer and fostering a collaborative codebase understanding.
contractNowTV (Sky UK)(Media)
senior developer
Nov 2018 - May 2019
  • Collaborated in an agile setup to alleviate technical debt, achieving a 5% efficiency gain in content delivery pipelines across multiple devices.
  • Enhanced testing protocols, leading to a 5% increase in coverage for both Jest unit tests and Ruby-based functional tests.
  • Developed and deployed new features such as a VOD content rail, and orchestrated a custom A/B testing framework using Optimizely.
contractuSwitch(ecommerce)
senior frontend developer
Aug 2018 - Oct 2018
  • Integrated a 3D Secure verification process within the broadband switch journey, utilizing the Broadband Checker, resulting in a 15% uplift in conversion rates.
  • Accelerated cypress-based smoke test speeds by 40% by employing a record and replay strategy for API responses.
contractThe Sun (News UK)(Education)
full stack developer
Mar 2018 - Aug 2018
  • Developed interactive features such as live sports metrics and video galleries, significantly enhancing user engagement on The Sun's digital platform.
  • Successfully orchestrated the launch of the 2018 FIFA World Cup feature page, catering to peak viewership of over 2 million.
  • Implemented performance optimizations and tracking enhancements, leading to more efficient ad loading via header bidding and granular insights into user metrics.
contractAIG(Insurance)
frontend developer
Nov 2017 - Feb 2018
  • Contributed to a contract-centric multi-tenancy insurance quote generation platform, enhancing business efficiency and customer service.
  • Implemented Redux-Saga for effective management of asynchronous API interactions, ensuring a smooth user experience.
  • Utilized memoization strategies to maintain optimal performance during the quote generation process.
contractThird Space Learning(Education)
full stack developer
Aug 2017 - Oct 2017
  • Developed and optimized a suite of interactive React and Apollo-based educational applications, enhancing learning engagement and outcomes.
  • Standardized front-end development with Styled-JSX, improving design consistency and streamlining UI component creation.
  • Led the integration of GraphQL services, enabling real-time data exchange and dynamic content presentation.
permanentBeamly(Media)
software engineer
Nov 2016 - Aug 2017
  • Orchestrated the front-end engineering of interactive marketing campaign platforms, driving user engagement and providing actionable insights through data analytics.
  • Pioneered the adoption of responsive design methodologies, achieving seamless cross-platform user experiences and increasing campaign reach.
  • Optimized page load times by implementing advanced front-end optimization techniques, leading to a 30% improvement in performance metrics.
permanentKano Computing(Education)
software engineer
Jul 2015 - Oct 2016
  • Enhanced the user onboarding experience for the Kano web platform by streamlining the process with user-tested improvements.
  • Co-developed the Kano web store with Vue.js, Shopify, and Node.js, enhancing e-commerce functionality and user interface.
  • Implemented internal services like a delivery times estimator and a product bundler on top of Shopify, optimizing promotional activities for the marketing team.
permanentLearn Forward(Education)
software engineer
Apr 2014 - May 2015
  • Contributed to the content team by crafting interactive and collaborative textbooks for students, utilizing Backbone.js, Jade, Stylus, and our open-source authoring tool LFA.
  • Played a pivotal role in the 2014 Romanian Presidential campaign by developing the website for candidate Monica Macovei, demonstrating proficiency in modern web development practices.
  • Enhanced digital platform user experiences and efficiency through strategic improvements in performance and comprehensive usage tracking.

Key Highlights

BSc in Computer Science from University of Bucharest
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