Javascript Engineer (IV-V)

Confiant•New York, NY

3d•$140,000 - $220,000•Remote

About The Position

We are seeking an experienced JavaScript Engineer to be part of the team that owns and evolves the core client-side SDK that sits at the heart of Confiant's malvertising detection and blocking technology. This is a deeply technical, specialized role focused on building and maintaining a high-performance JavaScript SDK that is embedded across a wide network of publisher and ad platform integrations. You will be engineering the invisible — precise, performant, and resilient JavaScript that executes in real-time within ad environments to detect and neutralize threats before they reach end users. The ideal candidate has a genuine passion for the craft of JavaScript at a systems level: understanding the browser runtime deeply, obsessing over payload size and execution cost, and building SDK distribution and versioning strategies that scale cleanly across a large, diverse customer base.

Requirements

Expert-level JavaScript (ES6+) with deep knowledge of browser internals — the event loop, memory model, garbage collection, and execution context
Strong understanding of how JavaScript executes within third-party and sandboxed environments (iframes, ad slots, cross-origin contexts)
Proven experience building, shipping, and maintaining JavaScript SDKs or embeddable scripts at production scale
Demonstrated ability to optimize for performance: bundle size, parse time, runtime efficiency, and network impact
Experience with SDK distribution patterns — versioning strategies, CDN delivery, backward compatibility, and graceful degradation
Proficiency with modern JavaScript tooling: bundlers (Webpack, Rollup, esbuild), transpilers (Babel/SWC), and testing frameworks (Jest, Playwright, or similar)
Deep familiarity with browser security models, including same-origin policy, CSP, and cross-origin isolation

Nice To Haves

Experience in AdTech, including familiarity with ad serving infrastructure, tag management, or programmatic advertising concepts
Background in security engineering, threat detection, or malware analysis
Experience instrumenting client-side SDKs for telemetry and observability
Familiarity with browser automation tools (e.g., Puppeteer, Playwright) for testing ad environments

Responsibilities

Co-own the design, development, and ongoing maintenance of Confiant's client-side JavaScript SDK with your teammates
Build and optimize SDK internals for maximum runtime performance — minimizing execution time, memory footprint, and impact on page load across diverse publisher environments
Develop robust SDK versioning, deployment, and distribution strategies that allow seamless rollouts and updates across a large, heterogeneous customer base
Translate security threat intelligence (e.g., new malvertising techniques, ad injection patterns) into SDK-level detection and blocking logic
Instrument the SDK for observability — ensuring signals, errors, and detection events are surfaced reliably back to Confiant's backend systems
Collaborate with the security research team to stay ahead of evolving malvertiser methods and rapidly prototype new detection heuristics
Conduct rigorous performance profiling, benchmarking, and regression testing to ensure SDK changes never degrade customer experience
Establish and champion SDK engineering best practices including testing strategies, documentation standards, and release processes
Debug complex, time-sensitive production issues occurring within live ad environments across a wide range of browsers and platforms