Senior Frontend Engineer – JavaScript / TypeScript

Remote – Europe (Eastern Europe preferred) | €50–€65 per hour | Initial 6-Month Contract

We're looking for a Senior Frontend Engineer to take ownership of a high-performance analytics SDK and customer-facing dashboard within a growing technology product.

This is a hands-on role suited to an engineer with strong JavaScript/TypeScript expertise, deep browser knowledge and a passion for performance, scalability and building reliable user experiences.

Key Responsibilities

  • Develop and optimise a lightweight, dependency-free vanilla JavaScript analytics SDK.

  • Build and maintain session recording, playback and event-streaming functionality.

  • Take a Python-backed fraud-monitoring dashboard from prototype to production.

  • Optimise browser performance, compatibility and bundle size.

  • Implement automated testing using Jest and Playwright.

  • Work with APIs, data contracts and BigQuery to ensure accurate, real-time data presentation.

Essential Requirements

  • 5+ years of commercial JavaScript/TypeScript experience, including 2+ years in performance-critical browser development.

  • Strong understanding of browser internals, event loops, timing and cross-origin contexts.

  • Experience maintaining or modifying third-party JavaScript libraries.

  • Build tooling experience with Rollup, Babel and bundle-size optimisation.

  • Strong testing experience with Jest, Playwright and CI/CD pipelines.

  • Experience building data-driven dashboards and working with APIs.

  • Comfortable with backend-adjacent development and Python-backed applications.

Nice to Have

  • Experience with bot detection, behavioural biometrics, browser fingerprinting or fraud prevention.

  • D3.js or other data visualisation experience.

  • BigQuery and Parquet knowledge.

  • Experience publishing and maintaining npm packages.

Contract Details

  • Location: Fully remote – Europe or US (Eastern Europe preferred, particularly Poland or Ukraine).

  • Rate: €50–€65 per hour, depending on experience (market rates considered).

  • Duration: Initial 6 months, with potential to extend.

  • Hours: 20–30 hours per week initially, potentially increasing.

  • Working Hours: Must be able to accommodate some US working hours.

  • Engagement: Freelancers welcome, including those currently working on other projects.

If you're a strong JavaScript/TypeScript engineer with a passion for browser performance and complex frontend engineering challenges, we'd love to hear from you!