Senior JavaScript Engineer (Full-stack, Retention)

This is a primarily back-end role (:70%) where you will design and evolve TypeScript services that power personalized replenishment, cross-sell, and subscription offers used by Shopify stores processing millions of transactions.

You will own features end-to-end, shaping the problem with a Senior Product Manager, proposing the architecture, implementing the solution with the support of AI, and monitoring and operating it in production. These systems need to be reliable, observable, maintainable, and performant.

You will effectively use AI agents such as Claude code and Codex to deliver at pace.

You will also contribute to our React-based front-ends (:30%) when delivering features as part of an experienced multi-functional team.

About The Product

Relo, a Relay company, helps consumer goods and subscription brands unlock more than 30% additional revenue from their existing customers. The platform gets one-time buyers to order again, turns more customers into subscribers, and keeps them loyal. It does this through an engine that predicts when each customer is ready to reorder, making recurring revenue easy for scaling Shopify merchants.

Primary Responsibilities

• Work as part of a skilled, AI-native, multi-disciplined product engineering team to rapidly deliver modern software, to excellent quality standards, across high-volume subscription and billing systems.
• Design and deliver serverless TypeScript services on AWS Lambda, backed by MySQL and Prisma ORM.
• Contribute to efficient, modern React applications which rely on our APIs and integrate with the Shopify and Klaviyo ecosystems.
• Own features end-to-end, working with your team to make sure we ship solutions to real customer problems.
• Support our Customer Success team by joining our working hours escalation schedule, operating and maintaining the live production system.
• Participate in architectural discussions and technical decision making across Relo and the rest of Relay Commerce.
• Add agent context to codebases, run coding agents, build MCPs and AI product features to open our platform to LLMs such as Shopify’s Sidekick.
• Contribute improvements to processes, guidelines, and documentation in a fully-remote organisation.

• You are comfortable taking loosely defined product ideas and turning them into concrete technical solutions.
• You effectively use AI agents such as Claude code or Codex to deliver working, reliable software at pace. You understand and can explain skills, MCP’s, RAG and other aspects of AI tooling. You know when to delegate to Claude and Codex, and when not to.
• You communicate clearly in writing. Design proposals, pull requests, and technical discussions should be concise and easy for other engineers to follow.
• You consider the operational impact of the systems you build. You think about reliability, observability, security, and performance before and during development.
• You are comfortable working across the stack when needed; front-end with React, back-end with REST APIs and CLI scripts, in the database, with infrastructure-as-code, or with cloud-native services.
• You take accountability for the systems you build and follow issues through to resolution with a high degree of quality control.

Required Expertise

We are looking for someone who can comfortably describe themselves as a Senior JavaScript Engineer (with significant experience using JS and TS full-stack), who is experienced in owning features from idea to delivery.

Technical

• Significant, proven, senior-level experience with JavaScript across multiple frameworks. Our guidance is a minimum of 8 years across multiple companies.
• Extensive experience designing REST APIs, especially for systems that integrate with third-party platforms.
• Deep expertise crafting TypeScript using class-oriented design, strong typing, SOLID principles, OOP patterns, and test-driven development.
• Strong SQL and relational database knowledge; understanding of query performance, indexing strategies, and schema design in MySQL or another RDBMS.
• Clear proficiency with React; able to implement components, build interactive UI, manage application state, and integrate cleanly with backend APIs.
• Experience with cloud-native services in Amazon Web Services.
• Highly desirable: Experience with predictive algorithms
• Highly desirable: Experience with the Shopify platform, structures, and data
• Highly desirable: Experience with SRE practices and observability tools like DataDog.

Product

• Delivery experience; you have defined and shipped major features as part of a team.
• Excellent written and verbal communication skills; you can deliver clear and succinct explanations of technical topics for a variety of audiences.
• Customer focus; you put customers, their needs, and their experience first., * Initial call (30 minutes). You’ll speak with our Engineering Manager for Relo, Joel Jenvey, discussing your approach to problem solving, engineering expertise, knowledge of JavaScript, and use of LLMs.

• Second round (1 hour 30 minutes) - You’ll meet with our Engineering Manager, Joel Jenvey again, and a colleague from the current Relo development team

We would like you to demonstrate your senior level of technical experience. We ask all hands-on team members to complete a refactoring exercise for 30mins with the interviewers.

We’ll discuss your technical assessment, and then move on to more specific questions about your skills and experience in technical areas.

• Final round (45 minutes) - You’ll meet with our CTO, Tom Russell, and our GM for Retention, Gauthier Derrien. They’ll be particularly interested in how you collaborate with non-engineering team members.

Benefits & Perks

• Flexible Time Off
• Public Holidays Off
• Paid Parental Leave
• Work From Home Stipend
• Therapy/Mental Health Reimbursement
• Co-working Space Allowance
• Company Swag

Relay Commerce is an equal opportunity employer. We celebrate diversity and are committed to creating an inclusive environment for all team members.

Relay Commerce is an e-commerce enablement platform offering scaling solutions across personalized messaging, social commerce, and customer retention, helping merchants navigate the rapidly evolving digital landscape with a comprehensive suite of tools. The Relay suite of solutions currently drives more than $1 billion in aggregate incremental gross merchandise volume for more than 35,000 merchants.