Lead CRO Developer (JavaScript)

Location: London, England, United Kingdom; hybrid office/home working with office attendance on Tuesdays and Thursdays.

Company

hirify.global is an experience design agency combining UX, design, insight, and experimentation to create customer experiences for B2C and B2B brands.

What you will do

• Build and ship A/B and multivariate experiments from supplied concepts, designs, and specifications.
• Develop experiment variations and functionality using JavaScript, HTML, CSS, React, and Next.js.
• Implement experiments across Optimizely, VWO, AB Tasty, Convert, Monetate, and similar enterprise platforms.
• Handle complex DOM manipulation, application state, targeting, customer journeys, dynamic content, feature flags, and server-side experiments.
• Implement and validate tracking, events, and data-layer requirements using GTM and Tealium.
• Debug experiment failures, performance issues, flicker, race conditions, and client-code conflicts while supporting other CRO developers.

Requirements

• Advanced JavaScript, including ES6+, Vanilla JavaScript, HTML5, CSS3, and CSS preprocessors such as SCSS.
• Strong hands-on Optimizely Web experience and extensive experience building and shipping live A/B and multivariate tests.
• Strong React and Next.js experience, including debugging single-page applications and dynamically rendered experiences.
• Excellent browser developer-tools, cross-browser and cross-device QA, debugging, REST API, AJAX, and Git skills.
• Experience with GTM or Tealium, event tracking, data layers, CMSs, ecommerce platforms, and varied client technology stacks.
• Ability to work independently on technically complex builds, communicate solutions clearly, and provide technical escalation support across multiple client accounts.

Nice to have

• TypeScript, Node.js, server-side or full-stack experimentation, SDK and API implementation, and feature flags.
• Experience resolving flicker or FOOC and other experiment performance issues.
• GA4 knowledge, high-traffic retail or ecommerce experience, and agency experience across multiple client codebases.
• Experience with Jira.

Culture & Benefits

• Hybrid office/home working.
• Enhanced maternity and paternity pay.
• Access to the Perkbox employee benefits platform.
• 25 days of annual leave.
• Professional growth and career development opportunities.
• Company updates, socials, and work in a dynamic agency environment.