Denis is available for hire
Hire DenisDenis Ok
Verified Expert in Engineering
Software Developer
Phnom Penh, Cambodia
Toptal member since March 9, 2016
Bio
Denis is a full-stack developer with a strong background in front-end technologies and UI/UX, and has recently turned his attention to React. A former software engineer at Microsoft, he delivered scalable projects used by millions. He contributed to the F# language and was the main contributor to Visual F# Power Tools. Denis invented a high-performance Loop 3D surface subdivision algorithm, built custom plugins and eCommerce sites, and synchronized systems across multiple devices for Xbox Music.
Portfolio
Defacto
Python, PostgreSQL, Terraform, React, Tailwind CSS, Material UI, TypeScript
The Foundry
React, TypeScript, Node.js, NGINX, Amazon Web Services (AWS), Docker, Next.js...
Toptal
React, Material UI, Figma, Functional Programming, HTML, JavaScript
Experience
- JavaScript - 7 years
- F# - 7 years
- HTML - 5 years
- MySQL - 5 years
- React - 5 years
- Azure - 4 years
- Angular - 2 years
- .NET Core - 2 years
Availability
Part-time
Preferred Environment
TypeScript, C#, F#, .NET, Azure, Visual Studio, React
The most amazing...
...project I've worked on is the Visual F# Power Tools, bringing a pleasant development experience to F# developers—as this wonderful language deserves it.
Work Experience
Senior Full-stack Engineer
2022 - 2024
Defacto
- Revamped the whole web app and integrated the new design from Figma to React/Material UI in 2022.
- Developed and maintained the client-facing front-end web app in React/TypeScript, especially the invoice/loan stories (special care with dates, user-friendly alerts for late repayment).
- Implemented diverse back-end API/integrations with partners (loan detection, POC, etc.).
- Reduced the loan recovery team's time spent per late repayer by automating the sending of legal formal notices and order for payment. Worked with our with IT service providers to adapt their APIs to our needs.
- Helped revamp the web app again for the 3rd UI edition, using React Remix and Tailwind in 2024.
Technologies: Python, PostgreSQL, Terraform, React, Tailwind CSS, Material UI, TypeScript
Senior Software Engineer
2020 - 2022
The Foundry
- Developed a construction eCommerce website using Strapi, a headless CMS as a GraphQL back end (configuration and extension using code), and Next.js for the front end.
- Implemented designs from Figma wireframes into code using Bootstrap and Material UI.
- Implemented JWT-based authentication using Facebook login and support for multiple user roles and permissions.
- Chose a React Context API instead of Redux for state management to account for less complexity and easier onboarding concerning other team members.
- Implemented mobile authentication using Twilio services.
- Delivered multiple UI/UX based on three user roles: unauthenticated, normal user, and supplier.
Technologies: React, TypeScript, Node.js, NGINX, Amazon Web Services (AWS), Docker, Next.js, Figma, Bootstrap, Material UI, Apollo, GraphQL, Twilio, Flexbox, Functional Programming, HTML, API Design, Full-stack, Headless CMS
Front-end Developer
2021 - 2021
Toptal
- Implemented Figma designs into real React web pages with pixel-perfect layout, using the Material UI library.
- Optimized a heavy and long list of data with virtualization using the react-window library.
- Conducted deep customization of Material-UI component's appearance.
Technologies: React, Material UI, Figma, Functional Programming, HTML, JavaScript
Senior Software Engineer
2020 - 2020
Okoone
- Joined an ongoing effort of porting a legacy LightSwitch C# web app to Angular/TypeScript for Clevy Links (https://clevylinks.com/), a logistics platform dashboard with a role-based authorization system.
- Rewrote some critical parts of the existing TypeScript code (Angular components).
- Implemented a code review process to the existing team and team coding guidelines (based on my former experiences).
- Enforced build and unit test checks on the existing Jenkins CI system.
- Created a baseline unit test suite for the existing code (about 100 tests).
- Developed a baseline end-to-end test suite based on Cypress.io for more complex UI scenarios ( around 20 tests) to serve as "learn by example" material to the junior and senior team members.
Technologies: Cypress, SQL, .NET, TypeScript, Angular, Flexbox, HTML, API Design, Full-stack
Senior Software Engineer
2020 - 2020
Contract with WriteLabel (Toptal Client)
- Coded a Kafka-based message processing microservice to create N-N mappings in a join table and keep entities synchronized when they are added (users and groups relationships), all written in F#.
- Performed some large refactoring tasks in the codebase, including SQL queries.
- Added unit tests to existing microservice code that was not written by myself, which thus required a lot of analysis and deep understanding of the business logic.
Technologies: ASP.NET Core, Azure, MySQL, F#, Functional Programming, Concurrent Programming, API Design
Back-end Developer
2018 - 2019
Comedy Wire
- Rewrote and simplified around 50 HTTP endpoints from the legacy Java back end to F#/ASP.NET Core.
- Implemented complex MySQL optimization (indexes and efficient query writing) for a database with millions of entries created per day.
Technologies: ASP.NET Core, MySQL, .NET Core, Azure, F#, Functional Programming, Concurrent Programming, API Design
Full-stack Software Developer
2015 - 2019
Agora Opinion (Freelance Work)
- Installed an IoT PHP back end connected to 300 voting devices for toilet cleanliness satisfaction, sending approximately 10,000 requests per day and having SMS and email alerts (data stored in a MySQL DB).
- Implemented the full front-end user experience using Laravel, AngularJS, supporting multiple roles like administrator, local administrator, and the standard user.
- Developed a HighCharts dashboard to visualize and filter votes data by day/week/month/year and geographic area.
- Implemented Azure WebJobs in F# to issue daily reports to customers with QoS requirements.
- Maintained and upgraded the MySQL database schema for a dashboard that serves almost 200 businesses and 800 users.
- Implemented UI web testing using the F# Canopy library (Lefthandedgoat.github.io/canopy).
Technologies: HTML, CSS, Azure, F#, AngularJS, JavaScript, Bootstrap, Laravel, PHP, Flexbox, Object-oriented Design (OOD), API Design, Full-stack
Software Developer
2012 - 2015
Microsoft
- Worked on the synchronization system across multiple devices (Xbox, Windows, Windows Phone, iPhone, and Android) for Xbox Music, a massively scalable music service used by millions of consumers and devices.
- Implemented the Xbox Video (Microsoft's video streaming service) watchlists system.
- Performed big-data processing and analysis to measure and ensure the quality of our cloud services.
- Implemented a feedback tool on the web client, enabling users to ask for a missing song in the music catalog.
- Developed an internal diagnostic tool to investigate issues on users' music and video collection.
Technologies: Cloud, JavaScript, AngularJS, SQL, Azure, F#, .NET, Object-oriented Design (OOD), Concurrent Programming
Software Engineer
2010 - 2012
Tactineo
- Assisted the development of WPF software for touch-screen devices.
- Implemented custom and touch-friendly UI elements.
- Guided a touch presentation timeline visualizer/editor.
Technologies: Windows Presentation Foundation (WPF), .NET, C#, Object-oriented Design (OOD)
Research Intern
2009 - 2009
Dassault Systemes
- Invented and developed a high-performance Loop 3D surface subdivision algorithm based on patches.
- Developed a plugin system for an in-house 3D mesh viewer.
- Worked on automatic 3D surface parameterization without edges.
Technologies: OpenGL, C++, Object-oriented Design (OOD), Concurrent Programming
Experience
Crazy Wild Wines
https://1drv.ms/u/s!AkjqocnedssYgtQp_qQ4ifKUTsaDywMy natural wine cellar company has a back end in F# (Azure Functions and WebJobs), which is connected to my accounting system and a personal OneDrive account.
It provides me with the KPIs that are necessary for my business:
• The inventory (e.g., How much stock is left for each bottle?), taking losses into account (stored in an Excel file), and the invoices using GraphQL queries to my accounting system.
• My profit/revenue for the month.
I browse the KPIs using a React Native mobile app, as I often move around the city in Phnom Penh.
It provides me with the KPIs that are necessary for my business:
• The inventory (e.g., How much stock is left for each bottle?), taking losses into account (stored in an Excel file), and the invoices using GraphQL queries to my accounting system.
• My profit/revenue for the month.
I browse the KPIs using a React Native mobile app, as I often move around the city in Phnom Penh.
Visual F# Power Tools
I was one of the main contributors to this wonderful F# development tool including refactoring, code generation, and so on.
F# 4.0 Language
https://github.com/Microsoft/visualfsharpI helped to implement new standard library API functions.
Toptal React Academy Project
The Toptal React Academy is an exclusive learning program that teaches the React framework to select members of the Toptal network. After a month of study, all graduates are tasked with completing a 30-40 hour final project to build and deliver a React app from scratch. The above is a walkthrough of my final project.
Education
2006 - 2010
Master's Degree in Mathematics & Operational Research
Ecole Centrale de Lyon - Lyon, France
Certifications
DECEMBER 2020 - PRESENT
Toptal React Academy Graduate
Toptal, LLC
FEBRUARY 2015 - PRESENT
Microsoft Specialist: Developing Azure Solutions
Microsoft
FEBRUARY 2015 - PRESENT
Microsoft Certified Professional
Microsoft
Skills
Libraries/APIs
LINQ, React, Highcharts, jQuery, Flexbox, OpenGL, Facebook API, Node.js
Tools
Visual Studio, Microsoft Visual Studio, NGINX, Figma, Terraform
Languages
F#, C#, JavaScript, TypeScript, HTML, CSS, PHP, C++, SQL, GraphQL, Python
Frameworks
AngularJS, .NET, ASP.NET, Laravel, Angular, Cypress, ASP.NET Core, Bootstrap, Windows Presentation Foundation (WPF), React Native, .NET Core, Next.js, Material UI, Tailwind CSS
Paradigms
Functional Programming, Object-oriented Design (OOD), Concurrent Programming, Agile Software Development
Platforms
Azure, Windows, Amazon Web Services (AWS), Docker, Twilio
Storage
MySQL, Neo4j, PostgreSQL
Other
Back-end, Full-stack, APIs, Domain-driven Design (DDD), Serverless, API Design, Headless CMS, Cloud, Apollo, Mathematics
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