Joonas Mertanen

@ Helsinki, Finland

joonas@catjam.fi
catjam.fi/cv
github.com/wyozi
Finnish / English

As a software developer with a product-focused approach, my main interest and focus lie in building software that users like and find useful. I strive to find solutions to real-world problems while also ensuring that the development process is as efficient as possible.

I have a diverse range of interests in technology, including building software for satellites, contributing to numerous open-source projects, and participating in hackathons. Lately, I have been particularly interested in exploring collaborative editing and the metaverse.

In my free time much of my time goes into becoming a glider pilot.

Highlighted technical skills

Typescript / React / Node (5 yrs.)
Postgres / SQL (5 yrs.)
Ruby / Rails (3 yrs.)
Kubernetes / Docker (3 yrs.)
NoSQL (3 yrs.)
AWS / GCP (3 yrs.)

Professional experience

Fullstack developeratCat Jam Oy

Aug 2021 - Present
Helsinki, Finland
  • Provided software development services to companies of various sizes in Finland as an independent consultant.
  • Developed a fullstack user management platform with microservices
  • Handled database migrations, SQL data analysis, and created interactive mapping tools, and dynamic templating tools
  • Researched and designed architecture for a CMS targeting system and built a successful prototype
  • Improved testing coverage, contributed to a cross-team component library, and wrote documentation
  • Built features to meet urgent customer needs and led expansion to microservices, establishing solid foundations along the way
  • Technologies: React, Typescript, Next.js, Supabase, AWS (S3, EBS, DocumentDB), Postgres, Prismic, Cypress, Jest, Mapbox, Turborepo, Github Actions
Selected projects

Map architecture design tool - 2022-2023

Used React components and hooks to build a library- like platform for the user to sketch out and design cranes, areas, and other construction site elements on top of a real-world 2D map. Mapbox was used as the underlying map library, and we built the React integration, designed the data structures and HTML5 interactions on top of that.

Status update PWA - 2023

Created an offline-capable Progressive Web Application for employees to be able to update their current status from remote locations. The working conditions were remote enough to necessitate robust handling of network slowness and failures. Additionally, some material had to be cached on the device to be readable even in offline conditions.

Building a dashboard for user data management - 2021-2022

Utilized Next.js to design and build a complete dashboard for user data management for a growing startup. The project involved building complex external-data driven forms, optimizing for mass amounts of data both in the frontend and the backend, and ensuring that personal data is handled securely. All frontend was built using React.

Architecture and MVP for a headless CMS targeting system - 2021-2022

As part of our project to create an internal messaging and intranet system using Prismic as the headless CMS, I led the development of a sophisticated audience targeting system. The system required a logical conditional filtering system that used OR/AND operators on top of chosen targeting parameters. Despite its complexity, we ensured that the user interface was simple to use for CMS users. Our team successfully designed and built a prototype that fulfilled all the functional requirements.

Lead backend developeratVideo.io

Feb 2021 - Jul 2021
Remote / San Francisco
  • Made platform scale up to 30M+ monthly active users
  • Led migration from Firestore to Postgres
  • Implemented monitoring/alerting system with Prometheus and Grafana and CI deployments with Github actions and Pulumi
  • Business impacts include improved development confidence, codebase self-documentation, new developer onboarding efficiency, GCP cost savings, reduced PII storage, reduced bugs, reduced customer frustration, and improved infrastructure visibility.
  • Technologies: Node.js (w/ Fastify), React, Next.js, Svelte, Postgres (w/ Prisma), Kubernetes, GCP, Pulumi, FFMPEG, Grafana, Prometheus, GitHub Actions

Software developeratSmartly.io

Apr 2018 - Feb 2021
Helsinki, Finland
  • Built automated ad video creative production tools to automate and scale advertising for customers
  • Was the leading architect for an internal software project to produce automated data analysis from customer data
  • Took over development of pre-general availability asset library and developed it into a system used by all Smartly customers
  • Handled migration of tens of millions of previously uploaded assets, fixing performance problems, and ensuring service scalability
  • Technologies: Node (w/ Koa), React, Typescript, Postgres, Kubernetes, Ruby on Rails, Sidekiq, AWS, FFMPEG, GitHub Actions, RabbitMQ, MongoDB, PHP, AWS (S3)
Selected projects

Video Template editor optimization - 2020

Solved various optimization problems in building a performance-intensive video editor in the browser. Involved finding and filing bugs in Chromium, getting familiar with React's performance profiler, and finding efficient methods for global React app state manipulation (with Redux).

Cross-team analytics project - 2019-2021

Acted as the technical lead for a project pulling analytics data from multiple teams' domains and summarising it in an actionable customer-facing presentation form. Project involved collaboration with designers and data analysts, and was successfully grown after my initial participation.

Asset management service and ecosystem integration - 2019

I took over the development of an asset library and management service that was built using Ruby on Rails. My responsibilities included developing core functionality such as authorization, metadata extraction, and scalable CRUD operations. In addition, I integrated the service into the Smartly ecosystem by designing the outfacing API and incorporating automatic metadata updates into RabbitMQ queues. Over time, asset management became a core part of Smartly's offerings, and a team was formed to support it.

Part-time blogger and open-sourcer

I try to contribute improvements, bug fixes and reports to open-source projects whenever there is a chance. My contributions can be found from my Github profile (some examples: here (PR) and here (issue)).

I also write about various niche (mostly) technical topics at catjam.fi/blog.

Education

BSc in Computer Science
Aalto University
2021