Sr./Staff JavaScript Developer - Web SDK

This role is suitable for a Senior to Staff-level JavaScript Developer with 8+ years of web development experience, including at least 3 years building and maintaining Web SDKs or analytics libraries. Required skills include advanced JavaScript and TypeScript, browser APIs, cross-browser compatibility, REST APIs, modern build tools, CI/CD, performance optimization, and security practices such as encryption, hashing, obfuscation, and data privacy. The candidate should be experienced in designing SDKs for device fingerprinting, behavioral analytics, data collection, and fraud detection, while also leading architecture, reviewing code, mentoring engineers, and collaborating across teams.

How would you design a browser-based Web SDK for collecting device and behavioral signals while minimizing its impact on page performance?

I would use a modular, lazy-loaded architecture with asynchronous collection, batching, and prioritized signal gathering. I would minimize main-thread work, avoid blocking rendering, and measure CPU, memory, network, and latency budgets with real-user and synthetic benchmarks.

What techniques would you use to generate a reliable device fingerprint across browsers while accounting for privacy limitations?

I would combine stable, permission-respecting signals such as browser capabilities, screen characteristics, platform metadata, and rendering behavior, then normalize and hash them server-side. The design should tolerate missing or changing signals, avoid invasive techniques, and clearly define retention and consent requirements.

How would you capture mouse, keyboard, and touch behavior without compromising security or user privacy?

I would collect derived behavioral features such as timing, velocity, pauses, and gesture patterns rather than raw sensitive content, especially for keyboard input. Data collection would be opt-in where required, minimized, encrypted in transit, and protected against accidental capture of passwords or personally identifiable information.

How would you make a JavaScript SDK compatible with different browsers, versions, and device types?

I would rely on capability detection rather than user-agent checks, provide graceful fallbacks, and isolate browser-specific implementations behind stable interfaces. A browser and device compatibility matrix, automated cross-browser testing, and real-world telemetry would help identify regressions.

What would your TypeScript API design look like for a developer-friendly Web SDK?

I would expose a small, stable, strongly typed public API with explicit initialization, configuration, lifecycle, and error-handling methods. Internals would remain private, defaults would be safe, and versioning, documentation, and backward-compatibility guarantees would be treated as part of the product.

How would you secure data collected by the SDK and prevent tampering or abuse?

I would use TLS, strict input validation, authenticated requests, replay protection, and server-side verification rather than trusting client-generated signals. Sensitive identifiers should be minimized, hashed or tokenized where appropriate, and any obfuscation should be understood as a deterrent rather than a security boundary.

How would you structure the SDK build and release pipeline using tools such as Rollup, Webpack, or Babel?

I would produce optimized, tree-shakeable bundles for supported environments, with separate development and production builds and carefully controlled polyfills. CI would run type checks, linting, unit tests, bundle-size checks, security scans, cross-browser tests, and automated versioned releases.

How would you diagnose and reduce SDK memory usage, CPU consumption, and network overhead?

I would profile with browser performance and memory tools, inspect event listeners, timers, allocations, and serialization costs, and establish regression budgets. Improvements could include throttling and debouncing events, sampling signals, batching payloads, compressing data, and releasing resources when collection ends.

How would you design the SDK’s communication with REST APIs in unreliable network conditions?

I would use versioned endpoints, compact validated payloads, timeouts, bounded retries with backoff, request identifiers, and idempotent server operations. The SDK should fail gracefully, avoid blocking the customer application, and provide observable error categories without exposing sensitive data.

How would you test a fraud-detection Web SDK and ensure changes do not reduce signal quality?

I would combine unit, integration, contract, cross-browser, device, performance, and security tests with controlled datasets and replayable interaction scenarios. Signal-quality metrics, false-positive and false-negative analysis, canary releases, and production telemetry would validate behavior without relying only on code coverage.

Oscilar is an AI Risk Decisioning™ company helping banks, fintechs, and digital businesses prevent fraud, manage credit risk, and strengthen compliance. As a Sr./Staff JavaScript Developer, you’ll lead the design and optimization of a high-performance Web SDK for device fingerprinting, identity verification, and behavioral analytics, including cross-browser testing, security, CI/CD, and mentoring. Work remotely with a modern stack featuring JavaScript, TypeScript, browser APIs, REST, Git, Webpack, Babel, and Rollup. The role offers $180K–$262.5K plus equity, unlimited PTO, comprehensive employer-paid health coverage in the US, and the opportunity to make the internet safer through high-impact, cutting-edge technology.