Senior Developer - UIO

We're looking for a Senior Developer to join our eCommerce Technical team, based from the NEXT Head Office in Leicestershire! The Role: Are you an experienced front-end specialist passionate about creating seamless, high-converting digital experiences? Our eCommerce Tech team is looking for a Senior Front-End Developer to help evolve an enterprise digital platform serving over 8 million customers globally. Supported by central tech teams, we build and manage the NEXT and Total Platform websites and mobile applications - all developed in-house. Joining our User Interface Optimisation Team, you will take a lead role in delivering high-impact functionality driven by Conversion Rate Optimisation (CRO), rigorous A/B testing, and deep customer journey analysis. In this position, you will work within an agile, collaborative team alongside talented developers to refine and build upon a quality-centric eCommerce platform. You will bridge technical execution and commercial strategy, using data-driven experimentation to shape customer-facing features that directly influence multi-million-pound product investment decisions. What You’ll Take On Experimental Feature Architecture: Maintain, architect, and deploy high-performing client-side experimental features within the Bloomreach Digital Experience Platform (DXP). You will build rapid, time-limited tests designed to achieve statistical significance and drive key business insights. Technical Execution & Overrides: Intercept, override, and inject custom features using HTML, CSS, and modern JavaScript. You will establish best practices for performance, ensuring injection scripts run smoothly without causing layout shifts, impacting Core Web Vitals, or creating technical debt for base platforms. Technical Leadership & Quality: Drive code quality, readability, and modularity across the team. You will lead code reviews, champion performance standards, and ensure web accessibility standards (WCAG) are met across all responsive viewports. Continuous Improvement: Continuously evaluate and modernise workflows and practices to maximize developer productivity, efficiency, and feature velocity. Collaboration & Stakeholder Management: Translate complex technical concepts clearly for non-technical commercial and product stakeholders. Mentor and guide mid-level and junior developers, and contribute to out-of-hours support during peak trading events (e.g., Black Friday and seasonal sales). What You’ll Bring: Core Techology Mastery: Deep, hands-on experience with modern JavaScript, semantic HTML5, and advanced CSS/SASS architecture. Framework Experience: Practical expertise with modern JavaScript frameworks and libraries. Experimentation & CRO: A solid understanding of client-side A/B testing, DOM manipulation/injection, and conversion rate optimisation principles. Performance & Accessibility: Proven success in optimizing Core Web Vitals, UI performance profiling, and WCAG accessibility standards. Analytics & Insight: Practical experience with web analytics platforms (e.g., Google Analytics 4) paired with strong analytical and problem-solving skills to assess experiment results. Leadership & Communication: A track record of mentoring junior and mid-level engineers, leading technical discussions, and presenting clearly to commercial partners. Collaborative Delivery: Experience working effectively within a large-scale, fast-paced, multifunctional technical environment across responsive, multi-viewport platforms. Bonus experience: Familiarity with Azure DevOps, service-oriented architecture, or enterprise DXPs like Bloomreach. Discover how you can shape the future of our eCommerce platforms and build a career with space to grow - apply now. #LI-NI1 #LI-Hybrid