Frontend Engineer (Performance & UI Rendering)

the opportunity to join the leading Spanish company in the IT sector, with more than 25 years of experience and one of the most solid track records as a provider of technological solutions for companies.

We are a growing company with more than 400 employees and offices in Logroño, Madrid, Barcelona, Seville, Bilbao and Valencia.

Since August 2013, we have been part of the IONOS Group, Europe's leading digitalisation partner for small and medium-sized companies.

In short, we are a multicultural team that’s passionate about technology, bringing our professional experience from over a dozen countries: Germany, Argentina, Spain, the United States, France, the Philippines, Italy, Poland, Portugal, the United Kingdom, Romania...

Mission

Transform Nextcloud Office into a high-performance, modern web-based productivity suite, going beyond traditional DOM-driven applications. You will own the look and feel of the product, ensuring that even the most complex documents and spreadsheets remain fast, smooth, and responsive under heavy load.

Responsibilities

Build new frontend features such as advanced charts, conditional formatting, and interactive document elements
Develop fast, responsive user interfaces using modern JavaScript
Ensure a smooth 60fps experience across all user interactions (scrolling, typing, zooming)
Move performance-critical rendering logic from the DOM to Canvas or hardware-accelerated technologies
Refactor legacy styles into a modern, performance-optimized CSS system based on variables (supporting dark mode and high-contrast themes)
Implement responsive UI patterns such as optimistic UI to improve perceived performance
Collaborate with other teams to optimize latency and real-time user experience
Leverage AI tools to accelerate development while focusing on performance, edge cases, and UI quality

Requirements

Technical

• Strong experience with modern JavaScript (ESNext)
• Deep understanding of DOM behavior and performance trade-offs
• Experience with Canvas API or rendering libraries (e.g., PixiJS or Fabric.js)
• Solid knowledge of frontend performance optimization techniques
• Experience using Web Workers to offload work from the main thread
• Experience with modern CSS and performance-oriented styling
• AI & Development
• Experience using AI-assisted development tools (e.g., Cursor or similar)
• Ability to use AI as a productivity multiplier without compromising code quality

Profile

Strong focus on smooth UI and rendering performance (60fps mindset)
High level of English proficiency, with strong communication skills in an international team environment
Attention to detail in user experience and visual quality
Background in demanding frontend environments (e.g., interactive apps, data visualization, or graphics-heavy web applications)
Pragmatic, execution-focused mindset

What We Offer

• Hybrid work model (with preference for our offices in Alcobendas, Valencia, Barcelona, Sevilla, or Logroño)
• Flexible working hours
• Flexible compensation package
• Discounts on Arsys products
• Discounts on technology brands
• Personalized training and development plans
• Biannual team events
• Access to advanced AI tools with no usage restrictions
• Challenging frontend problems in high-performance environments
• Engineering culture focused on quality, performance, and continuous improvement