Grzegorz Marzencki, Developer in Kraków, Poland
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Grzegorz Marzencki

Verified Expert  in Engineering

JavaScript Developer

Location
Kraków, Poland
Toptal Member Since
June 23, 2021

Grzegorz has experience leading teams and working as a CTO. He is an expert JavaScript developer and trainer with expertise in front-end architecture design and team leadership. He has delivered projects for startups (including an MVP that won business funding) and large tech companies like Microsoft, MongoDB, and Two Sigma. Grzegorz's strengths are team leadership, building scalable architectures, and delivering the highest quality code.

Portfolio

Freelance
Angular, AngularJS, React, Node.js, JavaScript Testing, JavaScript...
jstrainings.com
Angular, React, Node.js, JavaScript, JavaScript Testing, CSS, HTML, TypeScript...
MongoDB
TypeScript, Node.js, React, MongoDB, Terraform, Grafana, Kubernetes...

Experience

Availability

Full-time

Preferred Environment

WebStorm

The most amazing...

...product I've delivered was an MVP for a startup that got the company funding. I was later hired to build the development team from the ground up.

Work Experience

JavaScript Developer and Architect

2016 - PRESENT
Freelance
  • Assisted startups and FAANG companies as an architect, tech lead, and developer.
  • Designed front-end architecture and oversaw the entire delivery process (from idea to solution).
  • Led teams of designers and developers and worked closely with project owners.
Technologies: Angular, AngularJS, React, Node.js, JavaScript Testing, JavaScript, Team Management, CSS, HTML, TypeScript, MongoDB, REST, Webpack, Architecture, Web Architecture, Leadership, API Architecture, Technical Leadership, Third-party APIs, Third-party Integration, Accessibility, RxJS, GraphQL, Front-end, Front-end Architecture, Web Development, User Experience (UX), API Integration, User Interface (UI), WebApp, Startups, HTML5, CSS3, Sass, SCSS, Material Design, Software Architecture, NgRx, Redux, APIs, Team Leadership, Software Engineering, CTO, Front-end Development, ECMAScript (ES6), Next.js, NestJS, Software, Firebase, Amazon Web Services (AWS), Artificial Intelligence (AI), MERN Stack, Docker, Python, Full-stack

JavaScript Trainer

2015 - PRESENT
jstrainings.com
  • Delivered around 1,000 hours of technical training about JavaScript and web technologies.
  • Created training for people from companies such as (but not limited to): Orange, Ericsson, Nordea, and Comarch.
  • Authored a video course for Packt Publishing about JavaScript.
Technologies: Angular, React, Node.js, JavaScript, JavaScript Testing, CSS, HTML, TypeScript, MongoDB, REST, Webpack, Architecture, Web Architecture, Leadership, API Architecture, Technical Leadership, RxJS, Front-end, Front-end Architecture, Web Development, User Experience (UX), API Integration, User Interface (UI), WebApp, HTML5, CSS3, Software Architecture, APIs, Software Engineering, Front-end Development, ECMAScript (ES6), Software, Next.js, Prisma, MERN Stack, MEAN Stack, Full-stack

Senior Web Engineer

2022 - 2024
MongoDB
  • Rebuilt an existing webpage using TypeScript and Next.js, resulting in a Google performance score increase from 38% to 98%.
  • Built a service from scratch as a proof of concept for architecture that was later implemented in MongoDB's new web application.
  • Achieved scalability by creating generic, composable components and established modularity using Atomic Design principles.
Technologies: TypeScript, Node.js, React, MongoDB, Terraform, Grafana, Kubernetes, Amazon Web Services (AWS), Prometheus, MERN Stack, Tailwind CSS, Full-stack

CTO

2021 - 2022
Reconstruction US Inc.
  • Served as a team leader, managed the team's workload, prepared tasks, and oversaw talents.
  • Reframed the vision for technology and rebuilt the tech stack entirely.
  • Created strategies to hire excellent developers, which increased the velocity of the technical work by 10x.
  • Worked closely with the business team to create products that were well aligned with the business needs.
Technologies: JavaScript, TypeScript, Serverless Framework, Next.js, Serverless Architecture, Amazon Web Services (AWS), Serverless, CTO, React, Node.js, GraphQL, Startups, Education Technology (Edtech), MERN Stack, Full-stack, Planning

Senior JavaScript Developer

2015 - 2016
Codete
  • Developed an MVP in Angular for a German startup (video platform).
  • Redesigned architecture and implemented from scratch an enterprise application with migration from jQuery legacy code to React and Redux, ES6, Immutable.js, and Webpack.
  • Conducted a number of technical interviews for a JavaScript-related position.
  • Developed the enterprise application for a Norwegian company (AngularJS).
Technologies: JavaScript, Angular, React, AngularJS, Team Management, Webpack, CSS, HTML, TypeScript, REST, Architecture, Web Architecture, Leadership, API Architecture, Technical Leadership, Third-party APIs, Third-party Integration, RxJS, JavaScript Testing, Front-end, Front-end Architecture, Web Development, API Integration, User Interface (UI), WebApp, Startups, HTML5, CSS3, Sass, SCSS, Material Design, Software Architecture, Redux, APIs, Team Leadership, Software Engineering, D3.js, Front-end Development, ECMAScript (ES6), Software, MEAN Stack, Full-stack

Software Developer

2014 - 2015
Grape Up
  • Mentored the front-end team (German startup) to redesign AngularJS architecture.
  • Introduced AngularJS to the team of Apache Flex developers.
  • Created a set of internal tools for fast project setup.
Technologies: JavaScript, AngularJS, CSS, HTML, REST, Third-party APIs, Third-party Integration, Front-end, Web Development, API Integration, User Interface (UI), WebApp, CSS3, Less, Software Architecture, Redux, APIs, Software Engineering, Front-end Development, Software

Co-founder

2012 - 2013
Young Da Vinci
  • Created the company from scratch, including product prototyping, and hiring.
  • Prepared and conducted a number of courses on programming dedicated to youngsters.
  • Prepared and conducted a number of lectures for students.
Technologies: Team Management, Leadership, Startups, Software Engineering, Front-end Development, Software

Security Management System for High-risk Areas

https://jstrainings.com/security_system/video.html
Developed the prototype of a system (MVP for a startup) and led a team in developing a fully functional product. The project was a security monitoring system providing a dashboard for real-time management of devices placed in hazardous areas. The solution was based on RX streams.

Libraries/APIs

React, RxJS, REST APIs, Node.js, NgRx, D3.js

Tools

JavaScript Testing, WebStorm, Webpack, Terraform, Grafana, Prisma

Frameworks

Angular, WebApp, Next.js, Redux, Bootstrap, NestJS, Tailwind CSS, AngularJS, Serverless Framework

Languages

JavaScript, TypeScript, CSS, HTML, CSS3, HTML5, Less, Sass, SCSS, ECMAScript (ES6), Python 3, GraphQL, Python

Paradigms

REST, Web Architecture, API Architecture, MEAN Stack, Management, Serverless Architecture

Storage

MongoDB

Platforms

Firebase, Amazon Web Services (AWS), Kubernetes, Docker

Other

Team Management, Architecture, Leadership, Technical Leadership, Third-party APIs, Third-party Integration, Front-end, Front-end Architecture, Web Development, API Integration, User Interface (UI), Material Design, Software Engineering, Team Leadership, APIs, Software Architecture, Front-end Development, Software, MERN Stack, Full-stack, User Experience (UX), Startups, CTO, Generative Pre-trained Transformers (GPT), OpenAI GPT-4 API, OpenAI GPT-3 API, OpenAI, Large Language Models (LLMs), Machine Learning, Planning, Accessibility, Artificial Intelligence (AI), Prometheus, Serverless, Education Technology (Edtech)

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