Critical Mass is looking for a talented and motivated Senior Front-End Developer to join our technology team, responsible for delivering innovative, visually compelling, and high-performance web experiences using modern JavaScript technologies. This is a unique opportunity to work with a high-profile client, collaborating closely with design, UX, and engineering teams to create best in class digital communications and interactive experiences.

Please note this is a hybrid, contract position.

You will:

• Collaborate with designers and UX specialists to rapidly prototype and implement engaging user interactions
• Lead development using Vanilla JavaScript (no frameworks) and modern frontend standards
• Build and maintain components using technologies like React, Vue, and jQuery—all implemented in native JavaScript for optimal performance and extensibility
• Develop visually rich, interactive 3D animations utilizing WebGL and Three.js
• Create high impact web animations and transitions using GSAP/GreenSock
• Integrate dynamic content from JSON or markdown sources using Handlebars (HBS) templating
• Write modular, maintainable styles with SASS, leveraging its advanced capabilities for scalable CSS architecture
• Ensure cross device and cross browser compatibility, accessibility (WCAG), and optimal page performance.
• Mentor junior frontend developers and contribute to code reviews, documentation, and testing best practices.

You have:

• 5+ years of professional experience building consumer facing websites with advanced skills in Vanilla JavaScript
• Deep understanding of HTML5 with at least 5 years of experience
• Advanced expertise in CSS3, with a strong focus on styling, layout, and design
• Proficient in SASS for writing modular, maintainable, and scalable stylesheets
• Strong command of responsive design principles to ensure seamless experiences across all devices
• Proven expertise with GSAP/GreenSock or similar animation libraries to deliver smooth, high quality web animations
• Experience building interactive graphics or 3D web experiences using WebGL and Three.js
• Hands on experience with Handlebars (HBS) for dynamic templating, including ingestion of JSON and markdown sources
• Familiarity with React, Vue, and jQuery, including implementing these patterns with Vanilla JS
• Strong Git proficiency and experience with modern development workflows (CI/CD, terminal, etc.)
• Solid troubleshooting and performance optimization skills
• Strong communication skills and ability to work collaboratively in a distributed team environment
• Experience working with enterprise level CSS systems or custom extensible design languages
• Knowledge of web accessibility standards (WCAG) and best practices
• Familiarity with content management systems (CMS), such as Adobe Experience Manager (AEM), or API driven architectures
• Experience with build tools like Webpack and task runners

Bonus if you have:

• Experience with advanced CSS methodologies or custom extensible style languages
• Demonstrated ability to push the boundaries of web technology with innovative UI/UX
• Familiarity with content management systems (CMS), such as Adobe Experience Manager (AEM), or API driven architectures
• Agency experience

What We Offer:

• Global maternity and parental leave
• Competitive benefits packages
• Vacation, compassionate leave, sick days, and flex days
• Access to online services for families and new parents
• Diversity and Inclusion Board with 12 affinity groups
• Internal learning and development programs
• Enterprise-wide employee discounts

Critical Mass is an equal opportunity employer. 

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#avoidIf Canada based: https://www.canada.ca/en/services/finance/consumer-affairs.htmlIf U.K. based: https://www.gov.uk/consumer-protection-rightsIf Costa Rica based: https://www.consumo.go.cr/educacion_consumidor/consejos_practicos.aspx