Maciej Jastrzebski
React Native React Expert
Wrocław, Lower Silesian Voivodeship, Poland
Summary
🤩
Rockstar🎓
Top SchoolMaciej Jastrzebski is a React Native and React expert with 11 years of experience designing and delivering mobile apps, particularly iOS solutions, and currently coordinating teams and SDK development at Callstack. He blends deep native iOS knowledge (Swift, Objective-C, MVVM/MVC, Xcode profiling) with React Native/TypeScript expertise, driving performance audits and contributing to key open-source tooling like React Native Testing Library and the performance tool Reassure. Comfortable in client-facing and hiring roles, he translates technical trade-offs for non-technical stakeholders and leads small engineering teams. His background in .NET and Xamarin adds cross-platform perspective, and he’s shipped hobby iOS apps on the App Store—evidence of hands-on craftsmanship beyond consultancy.
11 years of coding experience
12 years of employment as a software developer
Bachelor of Science (BSc), Computer Science, Excelent (celujący), Bachelor of Science (BSc), Computer Science, Excelent (celujący) at Politechnika WrocławskaMaster of Arts (MA), International Business, Very good (bardzo dobry), Master of Arts (MA), International Business, Very good (bardzo dobry) at Uniwersytet Ekonomiczny we Wrocławiu
English, Spanish
Stackoverflow
3,704reputation
301kreached
18answers
10questions
swift
top-5%
error-handling
top-1%
dictionary
top-5%
Github Skills (21)
javascript10
performance-monitor10
react-native10
testing10
typescript10
performance-testing10
performance-analysis10
jestjs10
typescript-types10
error-handling10
typescripts10
react10
bash9
dictionary9
swift9
Programming languages (6)
Github contributions (5)
callstack/reassure
Mar 2022 - Jan 2023
Performance testing companion for React and React Native
Role in this project:
Performance Engineer
Performance EngineerContributions:19 releases, 304 reviews, 63 commits in 10 months
Contributions summary:Maciej primarily contributed to performance testing and analysis within the `reassure` repository. Their commits focused on modifying test scripts and configurations to gather, compare, and output performance results. Key changes included refactoring the test structure, modifying scripts for running and comparing tests, and enhancing the output format, including the addition of Markdown and JSON outputs. They also addressed improvements for test stability and made adjustments to the test environment to ensure measurement accuracy.
regressionreactreact-nativetestingperformance
callstack/react-native-testing-library
May 2020 - Jan 2023
🦉 Simple and complete React Native testing utilities that encourage good testing practices.
Role in this project:Mobile Developer
Mobile DeveloperContributions:47 releases, 899 reviews, 104 commits in 2 years 8 months
Contributions summary:Maciej's primary contribution involved adding a new functionality to the React Native testing library, which included a new operator 'within' for instance-bound queries to improve testing. They implemented the operator, added related tests, and updated relevant documentation. The user also added findBy\* queries for accessibility selectors, improved the getByTestId implementation and supported @testing-library/jest-native and the deprecation of old functions.
reactreact-native-testingjestreact-nativetesting
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