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 through deployment and production verification.
Strong written communication, collaboration, and problem-solving skills.

Preferred Qualifications

Ability to read and understand legacy applications built with .NET Framework and C#.
Experience working with SQL Server or comparable relational database platforms.
Familiarity with AWS, serverless computing, or other cloud application services.
Experience with payment platforms or other transaction-sensitive third-party integrations.
Experience with Playwright or a comparable browser-automation framework.
Familiarity with feature flags, phased cutovers, parallel operation, and strangler-pattern migrations.
Experience identifying undocumented behavior in legacy code and converting it into testable requirements.
Experience modernizing mature SaaS applications while maintaining production stability.
Familiarity with workflow-intensive software involving customer records, financial transactions, scheduling, or operational processes.
Experience establishing development standards that can be sustained by an internal engineering team.

Technology Environment

Frontend: React, TypeScript
Backend: Node.js, TypeScript, REST APIs
Existing Platform: Microsoft-based legacy application
Data: SQL Server and relational databases
Cloud: AWS and serverless services
Testing: Unit, integration, and browser-based automated testing
Delivery: Git, pull requests, code review, and CI/CD
Development Tools: AI-assisted coding and code-analysis tools
Core Competencies: Application Modernization, Incremental Migration, Data Integrity, Automated Testing, Production Stability, and Technical Documentation

What We Offer

Meaningful influence over the architecture and engineering practices of a major application-modernization initiative.
End-to-end ownership across planning, development, testing, deployment, and production validation.
The opportunity to establish standards for a modern React and Node.js platform.
Close collaboration with an established engineering team responsible for a mature, customer-facing SaaS application.
An engineering environment that supports thoughtful and responsible use of AI-assisted development tools.
Potential engagement extension based on performance and evolving business needs.

Interview Process

Recruiter Pre-Screen
Technical and Culture-Fit Interview with Engineering Leadership
Technical Interview and Live Coding with the Engineering Team

Originally posted on Himalayas

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

Job Description