Senior Full-Stack Engineer (Node.js, Typescript, React)

Role Overview We are seeking a Senior Full-Stack Engineer to help transition a mature, business-critical SaaS application from a legacy Microsoft technology stack to a modern React and Node.js architecture. This is a senior, hands-on role combining application development, technical design, and migration planning. You will work across the full stack—from user interfaces and APIs to business services and relational data—while helping the team replace existing functionality in controlled, production-safe increments. The ideal candidate has successfully modernized a live application and understands that effective migration requires more than rewriting code. You must be able to uncover existing business behavior, preserve data integrity, establish meaningful test coverage, and make pragmatic decisions that balance delivery speed with long-term maintainability. Location: Remote Key Responsibilities - Design and develop full-stack functionality using React, Node.js, and TypeScript. - Help shape the target architecture, project organization, development conventions, testing strategy, and delivery practices. - Transition complex business workflows from an established legacy application to the modern technology stack. - Build maintainable REST APIs, service-layer components, and data-access functionality with clearly defined responsibilities. - Break migration work into manageable, independently testable, and deployable increments. - Enable legacy and modern components to operate safely alongside one another during the transition. - Analyze existing code and workflows to identify and preserve important business rules, system behavior, and data relationships. - Write secure, parameterized SQL queries and optimize database interactions supporting transactional workflows. - Develop unit, integration, and end-to-end tests to confirm behavioral consistency and prevent regressions. - Produce modular, well-documented code and focused pull requests that are easy to review and maintain. - Apply appropriate migration safeguards, including staged releases, feature controls, monitoring, and rollback planning. - Use AI-assisted development tools to support codebase analysis, implementation, refactoring, and test development. - Evaluate AI-generated code carefully and take full responsibility for its correctness, security, and maintainability. - Collaborate with engineering leadership and developers through technical documentation, design discussions, and code reviews. - Investigate and resolve issues encountered during implementation, deployment, and production validation. - Establish sustainable engineering patterns that the internal team can maintain after the engagement. Required Qualifications - 7+ years of professional software development experience, including substantial full-stack responsibility. - Strong, recent experience developing production applications with React and TypeScript. - Strong backend development experience with Node.js and TypeScript. - Experience designing REST APIs, service layers, and maintainable data-access components. - Solid SQL and relational database expertise, including query development, optimization, and safe parameterization. - Hands-on experience modernizing, re-platforming, or incrementally replacing functionality within a live production system. - Understanding of migration approaches that minimize downtime, regressions, and disruption to users. - Strong automated-testing practices across unit and integration levels. - Experience with Git-based development, pull requests, peer review, and CI/CD workflows. - Practical experience using AI coding assistants as part of day-to-day software development. - Sound judgment when assessing AI-generated code for accuracy, security, maintainability, and unintended behavior. - Ability to document technical requirements, implementation plans, and architectural decisions clearly. - Demonstrated ownership from discovery and design throug