Critical Mass is hiring a

Senior ReactJS FrontEnd Developer - Temporary.

San José, Costa Rica

The Senior Front-End Developer (SFED) is responsible for designing and writing code and providing support to web applications. The SFED is able to work independently, assuming ownership for the design, interface and programming of simple and complex web sites.  The SFED should also be able to provide solutions and estimates for their tasks in support of his/her Tech Lead

The SFED works with web applications and a variety of front-end technologies including HTML5, CSS and JavaScript, and is comfortable with content management systems.


You will: 

  • Developing web applications that follow the latest web standards and conforms with leading-edge front-end technologies
  • Works closely with Creative, Business, Technology and QA teams to ensure the solution will meet the requirements and performance targets (mobile, desktop).
  • Owns the development of web applications and ensures they follow the overall technical architecture and design established by the technical lead
  • Implements user and business requirements which are composed of multiple development activities
  • Maintains up-to-date and complete documentation on projects as dictated by the capability’s guidelines and best practices
  • Debugs or troubleshoots complex issues in existing web applications
  • Proactively provide feedback on policies and procedures when an opportunity for improvement exists
  • Proactively provide guidance and support to other members of the in fulfill their tasks and improvement their performance and overall technical skills. 

You have: 

  • At least 4+ years of experience working with Front-End technologies, as ReactJs – JavaScript
  • Knowledge of Cross-browser and Responsive development
  • Work experience designing and developing web applications using HTML, CSS and JavaScript.
  • Understanding of recent development practices (Mobile First, MVC, Object Oriented development)
  • Work experience with cross-browser and cross-device compatibility
  • Proficiency using design tools (such as Photoshop, Illustrator, Figma and Sketch)
  • Work experience integrating with backend APIs and services.
  • Understanding of web design patterns (e.g., model-view-controller, observer, etc.) and modern web design practices (eg. Responsive Web Design)
  • Experience debugging or troubleshooting web applications, preferably using debugging tools such as browser-plugins, IDEs or debugging proxies.
  • Experience working with version control systems (like Git)
  • Work experience with data transfer formats popular in web applications (eg. JSON, XML)
  • Knowledge in accessibility and SEO best practices.
  • Knowledge in CSS pre processors (like SASS and LESS)
  • Knowledge and experience with AEM is a plus. 

What We Offer

  • Maternity and parental leave extra days
  • Competitive benefits packages
  • Vacation, compassionate leave, sick days, and flex days
  • Access to online services for families and new parents
  • End-of-year closure days (not deducted from vacation balance)
  • Diversity and Inclusion Board with 12 affinity groups
  • Internal learning and development programs
  • Enterprise-wide employee discounts
  • And more…

At Critical Mass, we value our employees and offer competitive compensation and benefits packages. If you’re looking for a challenging and rewarding opportunity to make a significant impact on the lives of our employees, we encourage you to apply for this exciting position today!

The Talent Team at Critical Mass is focused on ensuring we provide the best training, onboarding, and employee experience possible! Our new hires & employees are the future of our organization, and we want to set you up for long-term success. In an effort to do so, we expect our team to work from an office a minimum of 3 days a week.

Critical Mass is an equal opportunity employer that is committed to diversity and inclusion in the workplace. We do not tolerate discrimination on the basis of race, national origin, gender, gender identity, sexual orientation, protected veteran status, disability, age, or other legally protected status. If you are an individual with disabilities who would like to request an accommodation, please reach out to [email protected].

We are committed to fostering diversity, equity, and inclusion within our pool of candidates, with a target of achieving at least 50% representation from underrepresented communities.

The Critical Mass Talent Acquisition team will only communicate from email addresses that use the URLs criticalmass.com and us.greenhouse-mail.io. We will not use apps such as Facebook Messenger, WhatsApp, or Google Hangouts for communicating with you. We will never ask you to send us money, technology, or anything else to work for our company. If you believe you are the victim of a scam, please review your local government consumer protections guidance and reach out to them directly.

If U.S. based: https://www.consumer.ftc.gov/articles/job-scams#avoid
If Canada based: https://www.canada.ca/en/services/finance/consumer-affairs.html
If U.K. based: https://www.gov.uk/consumer-protection-rights
If Costa Rica based: https://www.consumo.go.cr/educacion_consumidor/consejos_practicos.aspx 

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