Rumen Han, Developer in Kingston, ON, Canada
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Rumen Han

Verified Expert  in Engineering

React and Django Developer

Kingston, ON, Canada
Toptal Member Since
November 9, 2018

Rumen has eight years of experience in web development using JavaScript (React, Angular), Python (Django), and AWS. He has worked on a variety of projects at companies of all sizes. He has been an important problem solver in the teams and has never failed to deliver quality work with his hard work and problem-solving skills. Rumen really cares about user-friendliness and the performance of your application.


React, JavaScript, TypeScript, Redux, Next.js, Express.js, TypeORM LLC (Via Toptal)
React, Redux, Redux Thunk, SCSS, JavaScript, Webpack, CSS
Care Of (via Toptal)
GraphQL, PostgreSQL, SendGrid, Node.js, SCSS, Bootstrap, NestJS, Boost, Apollo...




Preferred Environment

Atom, Visual Studio Code (VS Code), Windows 10, MacOS

The most amazing...

...thing I've contributed to is the Three.js project with React and Next.js. I used a lot of algorithms and proper data structures to speed up 3D model rendering.

Work Experience

Senior JavaScript Developer

2021 - 2023
  • Developed UI using React/Next.js and engaged in performance optimization.
  • Mainly focused on project management tools using Gantt charts.
  • Built reusable UI components using Storybook.
Technologies: React, JavaScript, TypeScript, Redux, Next.js, Express.js, TypeORM

Senior React Developer

2020 - 2021 LLC (Via Toptal)
  • Worked on the real-estate website with React, Redux, SCSS, Webpack.
  • Interpreted the Invision design into mobile-first responsive front-end UI.
  • Redesigned the websites from scratch using create-react-app and custom Webpack configuration.
  • Optimized React UI with lazy-loading and modern browser APIs.
  • Delivered new features and the storybook build component with optimization.
Technologies: React, Redux, Redux Thunk, SCSS, JavaScript, Webpack, CSS

Senior Full-stack Developer

2020 - 2020
Care Of (via Toptal)
  • Developed a Quora-like site using React, React Hooks front end with GraphQL for a home-care service company based in Australia.
  • Implemented mobile-responsive front-end pages with React, Bootstrap, and SCSS.
  • Used Apollo-boost to consume GraphQL API.
  • Engaged back-end development in Nest.js and PostgreSQL.
  • Integrated third-party APIs like Sendgrid.
Technologies: GraphQL, PostgreSQL, SendGrid, Node.js, SCSS, Bootstrap, NestJS, Boost, Apollo, React

Full-stack JavaScript Expert

2019 - 2019
Roubler Pte Ltd (via Toptal)
  • Developed USA’s leading cloud-based workforce management, HR, and payroll software with Angular, Node.js, Express.js, GraphQL, Apollo, PostgreSQL, Bootstrap, and more.
  • Worked closely with web development and software design team for production, modification, and maintenance of web applications.
  • Developed and unit-tested software that meets business requirements and technical design. Maintained code coverage quality for all new components built close to 90% with an emphasis on TDD.
  • Built great-looking software with technologies like Bootstrap to the dynamic back end in Socket.IO.
  • Troubleshot pre- and post-production implementations.
Technologies: React Native, AWS Lambda, RxJS, Bootstrap, PostgreSQL, Apollo, GraphQL, Express.js, Node.js, Angular

React, Node.js Developer

2019 - 2019
TRM Labs (via Toptal)
  • Joined the team as a React and Node.js developer with cryptocurrency experience.
  • Implemented React High-Order-Components along with Antd.
  • Implemented REST APIs with FeathersJS.
  • Wrote Blockchain-related helper functions.
  • Worked on the styling of React components along with Styled-components.
  • Used Enzyme, Jest, and Chai for the test and Lerna for packaging resources.
Technologies: Blockchain, MongoDB, Docker, Antd, FeathersJS, Node.js, Reselect, Redux-Saga, React

Remote Full-stack Developer

2019 - 2019
  • Developed Boston hospitals' medication provider search project using Django and React.
  • Implemented front-end pages using React and Redux Form.
  • Implemented REST APIs using Django REST framework and optimized Django ORM queries.
  • Fixed mobile responsive issue on server-side rendering in Next.js using JavaScript packages such as Lodash.throttle.
  • Integrated Django-packages like TinyMCE editor and customize Django admin behavior.
  • Fixed Django specific issues, maintained and upgraded Django packages.
  • Fixed cross-browser issues for the front-end including Chrome, IE, Firefox, and Safari.
Technologies: Django REST Framework, Django, Next.js, Mapbox, Redux Form, React

Full-stack Developer

2018 - 2018
  • Worked on Aurum's hotel inventory management web application with Angular. As the only developer, I had managed the design, development, and deployment of the project.
  • Implemented a real-time messaging system and custom calendar feature and other business logic using Firebase.
  • Implemented a notification system using Firebase Cloud messaging.
  • Added cloud functions with Node.js as back-end API management for handling database.
  • Implemented business logic and built responsive front-end pages with Bootstrap.
  • Deployed the project using Firebase hosting service with a custom user domain from GoDaddy.
Technologies: Firebase, React, Angular

Full-stack Developer

2014 - 2018
  • Contributed to multiple projects with React, Angular, Django, and AWS.
  • Built single-page applications with React (Redux-saga), AngularJS, and Angular.
  • Built React High-Order-Component to implement complement behavior and refactored JavaScript code.
  • Implemented optimized algorithms with the proper data structure to optimize rendering 3D models and its custom behavior in Node.js on a React project.
  • Implemented features and fixed issues in React-Redux-Form such as mobile-view rendering issue.
  • Worked on a Node and Redux-persist project with a lot of third-party APIs like Dropbox API and Google sheet API.
  • Worked on data visualization with HighCharts.
  • Wrote REST APIs with Django REST framework and Django server-side template with many other libraries like Djoser and django-allauth.
  • Deployed and managed a live development and production server. For instance, deployed a Django application in Ubuntu 16.04 machine with PostgreSQL and other tools and libraries like Celery, Elasticsearch, and Open Semantic Search.
  • Wrote a deployment script with NodeJS and bash shell script.
Technologies: Amazon Web Services (AWS), Firebase, Django, Node.js, Angular, React

Full-stack Developer

2012 - 2014
Altitude Labs
  • Built front-end pages with Bootstrap, JavaScript, HTML, and CSS.
  • Integrated a lot of data from different data sources like "world bank" to a database using Python packages such as Numpy and Pandas Data Reader.
  • Worked on an image processing project with OpenCV and JavaCV like crowd detection.
  • Contributed to JSP projects with Apache Tomcat.
  • Worked on WPF animation and desktop applications.
Technologies: C#, Java, Python, JavaScript

React, GraphQL Project

Developed a Quora-like site using React and React-Hook front-end with GraphQL and TypeScript for a home-care service company based in Australia.

Cloud-Based Workforce Management, HR, and Payroll Software
Developed USA’s leading cloud-based workforce management, HR, and payroll software with Angular, Node.js, Express.js, GraphQL, Apollo, PostgreSQL, Bootstrap, etc.

Data Analysis and Visualization Project

Developed project for the PowerforAll's data analysis project.
Integrated a lot of often source code to the Django project and auto indexing documents with opensemanticsearch tool and visualize data with HighCharts and Mapbox.

React, Mapbox, Django Project

Boston Hospital's medication provider search tool.
Implemented front-end pages with React, ReduxForm and developed REST APIs using DjangoRESTFramework and integrated many Django packages like tinyMCE editor and customized Django admin behavior

React, Three.js Project

Worked on a React.js project with Next.js framework.

Built front-end pages with React, Redux-Persist, Saga and display Dicom images using Three.js.

Code refactoring into ES7 and applying optimized algorithms to speed up rendering 3D models.

Hotel Inventory Management System

Developed hotel inventory management web application at Aurum. I designed, developed, and deployed the project with Angular 5 and Firebase back end


Python, HTML, CSS4, CSS, JavaScript, Python 3, ECMAScript (ES6), TypeScript, GraphQL, HTML5, Java, C#, SCSS


Cypress, Django REST Framework, Flask, Redux, Django, Angular, Express.js, MUI (formerly Material UI), Vuetify, FeathersJS, Bootstrap, Next.js, React Native, Boost, NestJS


Antd, REST APIs, Flask-RESTful, React, Node.js, Redux-Saga, ApexCharts.js, Vue, Highcharts, AmplifyJS, Vue 2, Redux Form, Reselect, RxJS, Three.js


MongoDB Atlas, Mongoose, Celery, Redux Thunk, SendGrid, Webpack, Atom


Android, Amazon Web Services (AWS), Firebase, Amazon EC2, Twilio, Google Cloud Platform (GCP), Docker, AWS Lambda, Blockchain, MacOS, Mapbox, Ethereum, Visual Studio Code (VS Code)


NoSQL, MySQL, PostgreSQL, Cloud Firestore, MongoDB, Elasticsearch


TypeORM, Hooks, Ajax, Material Design, Firebase Cloud Functions, Front-end, Blockchain Development, Apollo, Semantic UI, Microsoft Azure, Linux Administration, Progressive Web Applications (PWA), Windows 10



2007 - 2011

Bachelor's Degree in Computer Science

Chu Hai College of Higher Education - Hong Kong