Senior JavaScript Engineer

Responsibilities:

• Design and develop JavaScript-based monitoring agents that capture performance metrics, errors, and user interactions in the browser.
• Work with browser performance APIs (Navigation Timing, Paint Timing, Long Tasks, and Performance Observer) to track key metrics.
• Implement support for Core Web Vitals (LCP, FID, CLS, INP) and other industry-standard KPIs.
• Ensure that monitoring agents are lightweight, efficient, and non-intrusive.
• Collaborate with backend/APM teams to correlate frontend traces with backend monitoring data.
• Keep up with latest web performance standards and W3C specifications.

Requirements:

• 3+ years of professional JavaScript/TypeScript development experience.
• Strong expertise in browser APIs and event-driven programming.
• Hands-on experience with performance measurement and optimisation in web apps.
• Solid understanding of Core Web Vitals and web performance monitoring.
• Familiarity with cross-browser compatibility and web debugging tools.
• Experience with one or more frontend frameworks (React, Angular, Vue).
• Knowledge of compression techniques (gzip, brotli).
• Exposure to RUM or frontend monitoring tools (New Relic, Datadog RUM, Dynatrace, Sentry, etc. ).

Nice-to-Have Skills:

• Experience building or contributing to JavaScript SDKs/agents.
• Knowledge of Web Workers, Service Workers, and WebSockets.
• Familiarity with OpenTelemetry for frontend instrumentation.
• Understanding of privacy and compliance in telemetry (PII masking, GDPR considerations).
• Experience with session replay libraries and customisation.
• Prior contributions to observability, analytics, or APM solutions.

Skills

Core Web Vitals, JavaScript, TypeScript, browser APIs