Senior JavaScript Engineer

Know what really happens under the hood of a browser?

Can you walk through the JavaScript event loop in your sleep? Do you understand the browser rendering pipeline better than most devs understand their own code? Have you ever built your own JavaScript framework just for fun? Love open source? Then you might be exactly who we’re looking for.

This isn’t your run-of-the-mill TypeScript/JavaScript role. We’re not building landing pages or dashboards here. This is backend-level engineering that happens to run in the most hostile, performance-constrained environment there is: the browser.

We’re hiring a Senior TypeScript/JavaScript Engineer to own our browser-side JavaScript agent, CDN integrations, and performance-critical SDKs used by millions every day. You’ll be crafting tamper-resistant, lightning-fast code that survives in the wild—pushed to its limits by scale, security threats, and the quirks of every browser under the sun.

If you want to push the boundaries of what’s possible in the browser, apply today!  But first, check out our open-source projects to see if you can picture yourself here.

What You’ll Do

• Build and maintain our browser-side TypeScript/JavaScript agent used for device identification, bot detection, and risk assessment
• Engineer for stealth, resilience, and performance—minimizing footprint, resisting detection, and maintaining compatibility across browsers
• Optimize for both code size and execution speed in complex, adversarial environments
• Stay ahead of browser changes, plugin behaviors, and fingerprinting techniques
• Collaborate with backend, security, and data science teams to align signal capture with detection logic
• Write comprehensive tests and contribute to CI pipelines that ensure functionality across a wide range of platforms and devices
• Contribute to a widely-used open-source project with 24K+ GitHub stars and 25B+ monthly usages

What You Bring

• Expert-level JavaScript and TypeScript experience, especially in browser environments
• Deep understanding of browser APIs, DOM behavior, timing attacks, and anti-debugging techniques
• Experience building libraries or SDKs, especially for production or developer-facing use cases
• Strong frontend experience (~80%), with backend familiarity (~20%)
• Proficiency with build tools like Webpack, Rollup, Esbuild, including code obfuscation and minification
• Experience with modern testing frameworks such as Jasmine, Jest, or similar
• Familiarity with security principles, privacy best practices, and adversarial engineering
• Comfortable working in fast-paced environments without rigid specifications
• Strong sense of ownership and autonomy; you enjoy working independently and solving hard technical problems
• Clear written and verbal communication skills in English

Nice to Have

• Experience in complex domains like media, gamedev, or security, or on technically demanding browser projects (e.g. Google Docs, Figma, Miro, or 3D browser games)
• Contributions to open-source projects, especially in the JavaScript/TypeScript ecosystem
• Experience with WebAssembly, browser extensions, or remote debugging
• Familiarity with AWS services such as Lambda, CloudFront, and DynamoDB
• Browser automation or scraping experience

For US-based employees, the cash compensation range for this role is $140,000 – $190,000. We set standard ranges for all US roles based on function, level, and geographic location, benchmarked against similar stage growth companies. To comply with local legislation and provide greater transparency to candidates, we share salary ranges on all job postings regardless of desired hiring location. However, these ranges are specific to the hiring location and may differ within or outside the US. Final offer amounts are determined by multiple factors, including geographic location as well as candidate experience and expertise, and may vary from the amounts listed above.