Open to opportunities

Karlo Šeler

@karloseler

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Senior Frontend Engineer building high-performance, data-heavy SaaS user interfaces with React and Ember.

Croatia

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What I'm looking for

I want to build performance-focused, scalable UI for data-heavy SaaS—modernizing legacy code, delivering reusable design systems, and shipping production features on tight timelines with real-world constraints and collaboration.

I’m a Senior Frontend Engineer specializing in complex, data-heavy SaaS applications. I build high-impact user interfaces where performance, scalability, and real-world constraints matter—especially for planning tools, real-time collaboration, and large dataset visualizations.

At Productive.io, I delivered production-ready features under tight business timelines, simplifying complex task hierarchies and dependencies with data-heavy UI (Gantt, workload planning). I improved capacity planning and prevented overbooking, enabled scalable data collection with public forms tied to task creation and automation, and supported an upsell strategy through planning and automation capabilities.

I also modernized legacy systems and raised quality: I improved a legacy Ember.js codebase and enabled modernization (Embroider), and I optimized a canvas-based timeline module (Konva) for better performance and maintainability. Across product and platform teams, I strengthened frontend architecture through reusable components, design system contributions, and mentoring—alongside earlier work delivering and stabilizing UI in complex enterprise environments.

Experience

Work history, roles, and key accomplishments

Frontend Engineer

Productive.io

Jan 2023 - Dec 2025 (2 years 11 months)

Built data-heavy project planning UI (Gantt and workload views) to simplify task hierarchies and prevent overbooking. Modernized a legacy Ember.js codebase with Embroider, optimized a Konva timeline for performance, and delivered reusable components supporting a shared design system.

Gantt Charts Embroider Konva Canvas Timeline Optimization Design Systems UI Components Performance Optimization

Software Engineer

EPAM Systems

May 2022 - Jan 2023 (8 months)

Delivered UI enhancements and resolved production issues for the Click & Collect application. Supported reliable production releases via deployments, collaborated cross-functionally in an enterprise environment, and improved both developer and user documentation.

Deployment Enterprise Application Development Cross Functional Collaboration Technical Documentation User Documentation BAU (Business As Usual) Support

UI Developer

CloudSense Ltd.

Oct 2020 - May 2022 (1 year 7 months)

Improved consistency and development speed across Salesforce-based applications by building reusable form and grid UI component libraries. Contributed to internal design system tooling and documentation, mentored junior developers, and identified/resolved UI issues to maintain quality and stability.

Salesforce Development Component Libraries Grid Components Design Systems Mentoring

Junior UI Developer

CloudSense Ltd.

Jan 2020 - Oct 2020 (9 months)

Developed and optimized reusable UI components for Salesforce-based applications, improving performance and usability. Debugged and resolved frontend issues in production and contributed to reusable component architecture and the internal design system.

Junior Software Tester

CloudSense Ltd.

Jul 2018 - Jan 2020 (1 year 6 months)

Performed manual QA and regression testing across complex business applications. Identified and documented defects and partnered with developers to ensure timely resolution while learning user workflows and system edge cases.

Manual QA Testing Regression Testing Defect identification Edge Cases