Senior Front-End Developer (React)

Hastee, a Zellis company, is an award-winning fintech start-up providing a market-leading financial well-being solution. Our platform allows workers to get paid flexibly at any time of the month, provides money management and budgeting support, and helps them save sustainably. We deliver this in a B2B2C model, selling our solution to major employers, who in turn offer the Hastee app as a corporate benefit to their staff.  

Our revolutionary technology is designed to improve the productivity of the workforce and in turn, their organizations, and we are proud to have an NPS of 76 and 4.8/5 rating in the Apple Store and Google Play. Unsurprisingly, we’ve already won over 300 amazing clients, including McDonald’s, PayPal, and the NHS, and are now on a fantastic growth journey. 
Hastee was founded with a socially driven mission and has offices in Barcelona and London. We are backed by some of the leading fintech investors and are playing a crucial role in supporting workers affected by the cost-of-living crisis. 

Responsibility:  

• Lead the technical design and development of complex frontend features and applications using React. 

• Write clean, well-documented, and testable code following best practices and coding standards. 

• Collaborate closely with product managers, designers, and backend engineers to define and implement user interfaces and features. 

• Integrate frontend applications with backend APIs and services. 

• Optimize applications for maximum performance, scalability, and responsiveness. 

• Participate in code reviews, providing constructive feedback to team members. 

• Mentor and guide junior frontend developers, fostering their technical growth. 

• Stay up to date with the latest frontend technologies, trends, and best practices. 

• Contribute to the continuous improvement of our development processes and tools. 

• Troubleshoot and resolve frontend-related issues.

• Proven track record of 5+ years of professional experience in frontend development. 

• Extensive and deep expertise in React and its core principles. 

• Solid understanding of JavaScript (ES6+), HTML5, and CSS3. 

• Experience with modern frontend build tools and workflows (e.g. npm/yarn, Webpack, Babel). 

• Experience with RESTful APIs and asynchronous data handling. 

• Familiarity with testing frameworks (e.g., Jest, React Testing Library, Cypress). 

• Experience with version control systems (e.g., Git). 

• Excellent problem-solving, communication, and collaboration skills. 

• Strong communication skills and ability to collaborate in a remote-first environment.  

• Good in English (Spanish is a plus)  

• Nice to have knowledge of Fintech or payments-related development. 

Why Join Us: 

• Flexible work environment (hybrid or fully remote in the Spain). 

• Opportunity to work with cutting-edge technologies in a fast-growing fintech startup. 

• Strong engineering culture with a focus on quality, scalability, and innovation. 

• A supportive, diverse, and dynamic team that values growth and learning. 

• Work on a product that makes a real social impact on financial well-being.