Front end developer

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We are looking for a Mid-Senior level frontend / mobile developer based in the Netherlands to help our team develop innovative solutions and support the existing system.
At JOHAN Sports we guide sports teams to achieve higher performances and reduce injuries by combining Data Science and Sport Science. Data is collected from wearable devices and/or web forms (e.g., GPS/heart-rate trackers, WebApp, mobile applications).
Most clubs can’t afford or don’t have the know-how to work with a Performance Monitoring System. We focus on making such technologies affordable and easy to use for sports teams on all levels!

About Demcon

Recently acquired by Demcon, we are a small but ambitious group of people that still operates independently so you can expect a start-up environment while being backed by a well-rounded company. We are looking to expand our technical team and accelerate the development of the JOHAN Sports ecosystem.

As part of the front-end team, you will help with the maintenance and development of our web and mobile applications. You will collaborate with team members and parties (business, operations, back-end, sports scientist, and hardware developer) to discuss promising ideas and features, assess their technical feasibility, and translate them into solutions. You will most often own the feature/project you work on from ideation to production.

What are you going to do?

  • contributing to project specifications and assessing project impact in terms of resources and time
  • designing and writing code in web and mobile applications
  • spotting candidate technologies to support our development
  • when necessary, setting up contracts between developer parties (e.g., API, Doc)
  • Ensuring tests, documentation, and good practices via code reviews
  • Improving/Supporting pre-existing code.

Some example projects you could be working on:

  • Development of smart data visualisation for the web app using charting libraries, sourcing data from REST API.
  • Ingest/parse raw binary data from wearables via Bluetooth to be displayed to users using the mobile application.
  • Development of modules to collect data from players using the mobile application.
  • Development of new components like data filters in the web app as well as in the mobile applications
  • Development of flexible dashboards in the web app

What do you bring to the table?

Our web app is built on React JS, Redux, and other JS libraries (bundled in WebPack) which communicates with the backend via a REST API and WebSockets, some legacy code is still written in Angular JS, but React JS replaces it. Jest is used for testing the code. Our mobile applications are written on React Native and the backend is on Elixir/Phoenix and Python. CI/CD is managed through Terraform and CircleCI and our machines run at AWS. You’ll work with Jira to manage the workload, GitHub to work through pull requests from feature branches, and Confluence for the documentation of everything from initiative to development, plus the overall roadmap. We also use Grafana to see some server statistic information, Sentry to log both front-end and back-end errors, Paper trail to see server logs, and other useful online services, which help us to optimise our work processes.


  • 5+ years of experience with React (Web), React Native development (iOS and Android)
  • Expert in HTML and CSS and have experience with CSS-in-JS, CSS variables, and CSS precompilers
  • Experience with using REST web services
  • Experience with unit testing using Jest or comparable frameworks
  • Webpack knowledge
  • Experience with Git, JIRA

What do we offer you?

  • Possible to work from home 2 days a week
  • Work in a start-up environment backed by a well-rounded company
  • Short feedback loops with immediate insights from customer feedback
  • 31 days off and 8% holiday allowance
  • A good pension scheme
  • Phone allowance

Do you have any questions about this position?

Do you have any questions about this position? We will be happy to answer them. Call to  Niels van der Linden (Managing Director) at 088 115 2000

Have we aroused your interest for this position ? Then we look forward to receiving your cv. You can apply via the application button.

Acquisition based on this advertisement is not appreciated.

"bringing ambitious challenges to a success together."

application procedure.

Does this vacancy appeal to you and are you curious about the application process? This goes as follows:

1. Apply
You have applied! We will discuss it internally and respond as soon as possible.
2. Phone call
We got acquainted briefly and want to get to know each other better.
3. First call
See if there is a match from both sides and if the expectations are correct.
4. Second call
We investigate a possible collaboration more closely.
5. Offer
We both see the match! Let’s make you a suitable proposal.
6. Contract
Your response to the offer is positive. We are going to finalize the collaboration!