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Pavle Lekic
Verified Expert in Engineering
Full-stack Developer
Belgrade, Serbia
Toptal member since July 16, 2020
Bio
Pavle is a full-stack developer with more than a decade of experience building web apps, nine of which he spent on React-based projects. He is highly experienced with React and JavaScript in general. His passion is optimization—he loves making apps as optimal and performant as possible. Additionally, he possesses extensive knowledge of relational databases, with particular expertise in MySQL.
Portfolio
Brand Nudge Limited
JavaScript, React, Node.js, TypeScript, PostgreSQL, Redux, Workers, MSW...
Memory AS
React, TypeScript, Git, Front-end Development, Responsive, Redux...
Phia Holdings Inc
GraphQL, React, TypeScript, HTML5, CSS3, JavaScript, Redux, Next.js, Webpack...
Experience
- JavaScript - 12 years
- React - 9 years
- TypeScript - 7 years
- Jest - 6 years
- MySQL - 4 years
- Serverless - 3 years
- Amazon Web Services (AWS) - 3 years
- React Native - 2 years
Work Experience
Full-stack Developer
2025 - 2025
Brand Nudge Limited
- Partitioned a large products table to improve performance and wrote a procedure to manage and track data insertion progress.
- Profiled slow parts of the app and applied optimizations, reducing waiting time from 29 seconds to 0.16 seconds (around 180x improvement) when applying filters.
- Implemented offscreen rendering for charts to handle horizontal scrolling issues during screenshot exports and to ensure the best aspect ratio for each chart.
- Added end-to-end tests using Cypress that take and compare screenshots of charts.
Technologies: JavaScript, React, Node.js, TypeScript, PostgreSQL, Redux, Workers, MSW, Cypress, Profiling, Amazon Simple Queue Service (SQS), Database Partitioning, Docker, Relational Databases, Sequelize, Rendering Performance, Full-stack
Front-end Developer
2024 - 2025
Memory AS
- Implemented a new Export Report wizard, streamlining the user experience and enhancing functionality over the legacy solution.
- Reduced customer churn by resolving critical bugs, leveraging Sentry for error tracking and resolution, and working independently with minimal oversight.
- Enhanced UI/UX with iterative improvements, including dynamic date range support in DatePicker, complete revamp of the core HourStates feature, etc.
Technologies: React, TypeScript, Git, Front-end Development, Responsive, Redux, TanStack Table, Sentry, Turborepo, Vite
Full-stack React Developer (via Toptal)
2024 - 2024
Phia Holdings Inc
- Implemented a virtual list to enable smooth rendering of large amounts of data.
- Set up a Next.js app with Apollo GraphQL and a UI component library with Storybook inside the monorepo.
- Implemented components for the UI library, created the header, footer, sidebar, main results page, search overlay, added data fetching, etc.
Technologies: GraphQL, React, TypeScript, HTML5, CSS3, JavaScript, Redux, Next.js, Webpack, Node.js, Express.js, Apollo Client, Radix UI, Monorepos, Vercel, Apollo, React Apollo, Storybook, Cross-browser Compatibility, Responsive Web Design (RWD), Version Control, Full-stack
Full-stack Engineer
2020 - 2024
Gartner - Digital Markets Engineering - Capitalizable
- Created an optimal caching solution by dynamically invalidating only the parts of CloudFront cache that have changed.
- Wrote the clustering algorithm for the Capterra Shortlist page by analyzing the Google Maps clustering algorithm and adapting it for the products chart.
- Removed Next.js from the project by creating custom SSR logic, Babel, and Webpack configurations for the client and server, resulting in a 50% bundle size reduction.
- Wrote the Capterra.com Shortlist page, footer micro front end, parts of the header micro front end, the comparison tray, and parts of the category page (9+ million visits per month).
- Managed deployments to production and releases, and monitored AWS metrics/logs and cache hit rates.
- Wrote a scalable REST API using the Serverless framework (API Gateway and Lambdas).
- Integrated client and server-side error reporting to Rollbar, New Relic, and Datadog, and wrote integrations for Google and LinkedIn SSO.
Technologies: React, Node.js, Serverless, Serverless Framework, Amazon Web Services (AWS), Webpack, HTML, Cypress, Jest, Algorithms, Next.js, Front-end, HTML5, Web Development, Web Applications, APIs, Tailwind CSS, Figma, Git, Amazon S3 (AWS S3), Code Review, Test-driven Development (TDD), Software Engineering, Web App Development, Data Visualization, API Integration, JavaScript, Website Performance, TypeScript, Optimization, AWS Lambda, Google Tag Manager, Front-end Architecture, Full-stack Development, Lambda Functions, CSS3, Headless CMS, Cross-browser Compatibility, Responsive Web Design (RWD), Version Control, Microfrontends, Terraform, REST, Full-stack
Senior Front-end Engineer
2017 - 2020
HTEC Group Inc.
- Led the front-end and mobile team (six developers, including me) that developed an Uber-like app in just four months. Also served as a delivery manager for the whole project (20+ people).
- Developed a dynamic dashboard that can add/remove charts, rearrange, resize, and customize all aspects of each chart (chart type, axis, metrics, formatting, and ordering) and persist that on every change.
- Wrote a k-d tree cache for map features that drastically improved panning and zooming performance (we had 10,000+ objects on the map simultaneously).
- Improved the build process speed in watch mode by approximately 25x.
- Wrote an optimal zooming algorithm for routes that improved UX significantly.
- Wrote an algorithm to break large tables into separate pages in a smart way when generating large PDF reports.
- Added virtual lists that enabled us to handle huge amounts of data in the app without sacrificing performance.
Technologies: JavaScript, React Native, Redux, React, Jest, TypeScript, REST, Amazon Web Services (AWS), Cypress, Webpack, Front-end, HTML5, Web Development, Web Applications, Web Dashboards, Tailwind CSS, Figma, Git, Amazon S3 (AWS S3), Code Review, Test-driven Development (TDD), MUI CSS, Dashboards, Reports, Software Engineering, Web App Development, Data Visualization, PDF, API Integration, Leadership, CSS, Website Performance, Optimization, Front-end Architecture, CSS3, Cross-browser Compatibility, Responsive Web Design (RWD), Version Control, Sentry, Redux Toolkit, React Router, Rendering Performance
Senior Front-end Architect
2016 - 2017
Arbor Education
- Guided the overall design of the Arbor mobile app and implemented the main features of the app, like the calendar with all the teacher's classes/events.
- Applied optimizations to maintain good performance even on low-end devices.
- Implemented a custom mechanism to update the app over-the-air and bypassing the app store.
Technologies: JavaScript, Redux, React Native, Jest, Webpack, Front-end, HTML5, Web Development, Web Applications, Git, Code Review, Test-driven Development (TDD), Dashboards, Software Engineering, Web App Development, API Integration, CSS, Website Performance, Optimization, Front-end Architecture, CSS3, Version Control, Rendering Performance
JavaScript Developer
2015 - 2015
Teletrader
- Made several performance optimizations that improved rendering speed while panning by 25%.
- Tracked and fixed bugs using Jira as a reporting tool.
- Developed features and participated in design discussions.
Technologies: JavaScript, Front-end, HTML5, Web Development, Web Applications, Git, Code Review, Software Engineering, Web App Development, Data Visualization, API Integration, CSS, Website Performance, Optimization, Front-end Architecture, CSS3, Cross-browser Compatibility, Responsive Web Design (RWD), Version Control
Senior JavaScript Engineer
2015 - 2015
InterVenture
- Set up a webpack for a new React project using ES6 and hot reloading.
- Created stores and actions using the original Flux pattern.
- Wrote reusable components, several pages, and the data access layer.
Technologies: JavaScript, React, Webpack, Front-end, HTML5, Web Development, Web Applications, Web Dashboards, Git, Code Review, Software Engineering, Web App Development, API Integration, CSS, Website Performance, Front-end Architecture, CSS3, Cross-browser Compatibility, Responsive Web Design (RWD), Version Control
PHP Developer
2013 - 2014
First Beat Media Inc.
- Rewrote existing statistics reports to do all calculations in SQL, which simplified the logic significantly.
- Built several WordPress plugins and tweaked themes for high-traffic websites like citiesjournal.com with 9,000+ requests per minute.
- Created complex SQL queries (100+ lines of SQL, single select statement), stored procedures, triggers, and functions for various reports/cron scripts.
Technologies: JavaScript, MySQL, PHP, HTML5, Web Development, Web Applications, Web Dashboards, Git, REST APIs, Back-end, Dashboards, Software Engineering, Web App Development, SQL, CSS, Relational Databases, Website Performance, Relational Database Design, PHP 5, CSS3, Database Design, Version Control, Full-stack
Experience
OrbitMI
https://www.orbitmi.com/A React-based web app for managing fleets of vessels. I was one of the front-end engineers on the project. I developed several features and was in charge of optimizing the app's performance. Key improvements to which I contributed were the implementation of the k-d tree cache and improvement of the build process speed by 25x.
Skyryse Mobile App
https://skyryse.com/A React Native app for scheduling flights/transportation from A to B, very similar to the Uber app. I led a team of six developers and served as a delivery manager for the whole project (20+ people). I wrote the more complex parts of the app, like the optimal zooming algorithm for routes.
Leaf Logistics Web Apps
A React-based client and admin web apps for freight planning and execution. I was one of the front-end engineers on the project. I was tasked with developing several features, the most interesting one of which was a dynamic dashboard that is customizable in every possible aspect.
Arbor Mobile App
https://arbor-education.com/A React Native app for school teachers, like a digital diary. I was a front-end architect there. My primary responsibility was to guide the architecture/design of the app in the right direction, make smart tradeoffs, write the app's main features like the calendar with classes and events, and create a component library that would be used throughout the app.
Skills
Libraries/APIs
React, React Router, Node.js, React Testing Library, REST APIs, jQuery, jQuery UI, Apollo Client, TanStack Table
Tools
Webpack, Git, Figma, React Apollo, Sentry, Redux Toolkit, Amazon Simple Queue Service (SQS), Terraform, Sequelize
Languages
JavaScript, HTML, CSS, SQL, TypeScript, HTML5, PHP 5, CSS3, PHP, GraphQL
Frameworks
Redux, Serverless Framework, React Native, Cypress, Next.js, Tailwind CSS, Jest, Express.js, Material UI, MUI CSS
Paradigms
Test-driven Development (TDD), Responsive Web Design (RWD), Database Design, Microfrontends, REST, Responsive
Storage
MySQL, Amazon S3 (AWS S3), Relational Databases, SQL Performance, Database Performance, PostgreSQL
Platforms
AWS Lambda, Amazon Web Services (AWS), Vercel, Docker
Other
Front-end Architecture, Front-end Development, Relational Database Design, Rendering Performance, Front-end, Web Development, Web Applications, Web Dashboards, Code Review, Dashboards, Software Engineering, Web App Development, API Integration, Version Control, Website Performance, Semantic UI, Serverless, Full-stack, Full-stack Development, APIs, Lambda Functions, Back-end, Data Visualization, Headless CMS, Cross-browser Compatibility, Enzyme, Optimization, Algorithms, Google Tag Manager, Reports, PDF, Leadership, Radix UI, Monorepos, Apollo, Storybook, Turborepo, Vite, Workers, MSW, Profiling, Database Partitioning
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