Jörn Zaefferer
Engineering Manager at tonies® - Boxine GmbH
Cologne, North Rhine-Westphalia, Germany
Summary
🤩
Rockstar
Top expert inJavaScript Ecosystem Development
Jörn Zaefferer is an experienced engineering manager and hands-on developer with 19 years in web and open-source software, currently leading engineering at tonies® in Cologne. He built and led the software team at sloppy.io, shipping a container-as-a-service product that simplified Docker deployments for freelancers and agencies. A long-time contributor and project lead within the jQuery ecosystem, his work spans core libraries, QUnit testing, and tooling—impacting millions of web developers. He combines front-end craftsmanship (plugins, theming, UI) with test automation, build/release improvements and internationalization efforts across many high-profile repositories. As a consultant he ran 30+ client engagements, often acting as project lead, which honed his ability to translate complex requirements into maintainable code and processes. Colleagues know him for pragmatic engineering decisions and a rare depth in JavaScript testing and tooling that quietly improves developer workflows.
19 years of coding experience
9 years of employment as a software developer
English, German
Stackoverflow
5,695reputation
867kreached
44answers
4questions
tdd
top-1%
css
top-5%
jquery-validate
top-5%
validation
top-1%
unit-testing
top-5%
jquery
top-1%
Github Skills (49)
unit-testing10
javascript10
jquery10
theming10
testing10
plugin-development10
css10
internationalization10
user-interface10
ui-design10
validation10
graphical-user-interface10
gruntjs10
uid10
dom-manipulation10
Programming languages (22)
Github contributions (5)
jzaefferer/jquery-treeview
Oct 2010 - Jan 2017
A jQuery Tree plugin
Role in this project:
Front-end Developer
Front-end DeveloperContributions:19 commits, 4 PRs, 4 pushes in 6 years 4 months
Contributions summary:Jörn primarily focused on maintaining and updating the jQuery Treeview plugin. Their contributions included cleaning up demo code, fixing issues related to the combination of the "persist" and "prerendered" options, and updating the project to newer versions of jQuery. The user also removed deprecated code and updated the license information. The changes show an understanding of the plugin's inner workings and a dedication to maintaining its compatibility.
javascriptjquery-pluginjquery
jquery-validation/jquery-validation
Aug 2009 - Sep 2015
jQuery Validation Plugin library sources
Role in this project:Localization Specialist
Localization SpecialistContributions:3 releases, 289 commits, 44 PRs in 6 years 2 months
Contributions summary:Jörn contributed by adding and updating localization files for the jQuery Validation Plugin. The commits involved adding Persian (FA), and updating Swedish (SE), and Portugese (PT_PT) translations, and adding the relevant methods and messages files for German (DE), Dutch (NL) and Brazilian Portuguese (PT_BR). These changes aimed at expanding the plugin's international support and improving user experience in multiple languages.
inline-validationjqueryvalidationjavascriptjquery-validation-plugin
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