We are seeking a Senior Frontend Developer (JavaScript) who is highly skilled in building robust, scalable, and high-performance web applications using pure JavaScript (ES6+). The ideal candidate should have strong problem-solving skills, a solid foundation in JavaScript, DOM manipulation, and event handling, along with the ability to debug and resolve technical issues. This role involves supporting clients, ensuring smooth implementation of A/B testing solutions, and collaborating with internal teams to deliver an excellent customer experience.

Key Responsibilities

• Provide technical support in the implementation of A/B tests and personalisation campaigns, including dynamic content (e.g. Angular, React.js), custom JS scripts and integrations
• Develop and maintain complex client-side applications using Vanilla JavaScript (ES6+).
• Manage and evaluate client requests and liaise with partner/product teams as required
• Analyse, identify and evaluate new optimisation opportunities from technical,analytical or qualitative sources
• Support the Customer Success team with technical pre-sales and new client onboarding
• Conduct campaign feasibility studies and propose the best solution to meet the client’s needs within the capabilities of the tool

What you’ll Bring

• 3+ years of experience in front-end development with a strong emphasis on Vanilla JavaScript.
• Deep understanding of the DOM, event handling, closures, and asynchronous programming (Promises, async/await).
• Proficient in HTML5 and CSS3, with a strong eye for detail and responsive design.
• Strong debugging and problem-solving skills.
• Studies in web design, IT, usability/UX and development (especially with TypeScript)
• Thoughtful and a deep learner. You’re an analytical thinker who can apply your knowledge to a variety of technical contexts in a creative and goal- oriented way. You’re structured and creative enough to solve most challenging problems independently, given the necessary knowledge. You are a fast learner of new concepts and skills and love to dig deep
• Passion for the field. Curiosity and willingness to learn about new web and online marketing technologies
• Team spirit. You are a team player who is willing to share ideas and experiences and bring constructive ideas to the team
• Fluency in English. Effective communication is a key aspect of this role. That’s why you’ll need to be fluent in reading, writing and speaking English
• Strong understanding of monitoring DOM changes and element visibility for dynamic updates and manipulations (e.g., using MutationObserver, IntersectionObserver)
• Ability to write efficient functions
• Good knowledge of browser behavior, event bubbling, and event priority (mousedown, click, dblclick).

Preferred Qualifications

• Experience with AB Testing, Optimizely, or other experimentation/personalization platforms.
• Knowledge of HTML5, CSS3, and responsive design.
• Basic understanding of web performance and optimization.
• Previous experience in a technical support or frontend development
• Excellent communication and client-handling skills.