Open to opportunities

Kostiantyn Filimonov

@kostiantynfilimonov

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Senior Frontend Engineer with 10+ years building scalable e-commerce SPAs and AI-native workflows.

Ukraine

Message

What I'm looking for

I’m looking to lead frontend teams building scalable, high-load e-commerce platforms, combining solid SPA architecture with AI-native engineering workflows, strong performance optimization, and fast delivery from greenfield through migration.

I’m a Senior Frontend Engineer with 10+ years building scalable e-commerce platforms and high-load web applications. I architect complex SPA systems across React, Vue, and React Native, and I’ve pioneered AI-native engineering workflows to accelerate delivery.

At Jiffy.com, I led AI-Native Workflow efforts that achieved a “10x developer output” by integrating Cursor, Claude Code, and multi-agent systems into the SDLC. I built an AI PR orchestrator to manage concurrent Pull Requests, resolve logic conflicts, and flag UI regressions, then delivered a greenfield Checkout system in just 1 month. I also engineered and launched the Jiffy Android app from scratch and led the migration of the Shopping Cart from legacy Angular to a modern Vue.js stack.

I optimize for performance at scale—improving Core Web Vitals with Partytown.js (offloading 3rd-party scripts) and establishing monitoring with MixPanel—while leading teams through mentoring, architecture design, Agile/Scrum, and rigorous code review standards.

Experience

Work history, roles, and key accomplishments

Senior Frontend Engineer

Jiffy.com

Sep 2021 - Mar 2026 (4 years 6 months)

Led AI-native engineering workflows, integrating Cursor, Claude Code, and multi-agent systems to achieve 10x developer output. Migrated Shopping Cart from Angular to Vue, rebuilt Checkout in 1 month, and improved Core Web Vitals using Partytown.js while integrating native mobile payment flows (Stripe, Braintree, ApplePay).

React Vue.Js React Native Next.js TypeScript AI Development Partytown.Js Mixpanel

Frontend Developer

Smile

Apr 2018 - Sep 2021 (3 years 5 months)

Developed a React/Redux B2B e-commerce shop with a dynamic form generator supporting 1,000+ fields and lag-free UI. Built a viral PWA web game using Next.js and the Google Maps API, and evolved the platform architecture using Vue.js/Nuxt middleware layers.

React Redux Next.js Vue.Js Nuxt.Js Google Maps PWA jQuery Performance Optimization

Frontend Developer / Team Lead

Web-Systems

Nov 2015 - Mar 2018 (2 years 4 months)

Led the transition from static HTML/CSS to SPAs using Ember.js and React, and headed the front-end department for dozens of projects. Delivered a job search portal and an agrotechnology platform while maintaining front-end standards.

Ember.Js React Frontend Architecture Team Leadership HTML CSS Web Applications

HTML Coder

Web-Mosaica

Oct 2014 - Nov 2015 (1 year 1 month)

Delivered pixel-perfect layouts for 100+ landing pages from PSD designs. Wrote simple PHP email-notification scripting and implemented JS/jQuery interactions.

HTML CSS PSD To HTML JavaScript jQuery PHP Notifications Landing Pages