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Eugene is a faith-centric technologist, a serial entrepreneur, angel investor, advisor, and mentor. He is the founder and CEO of REACTIVE LIONS INC.

A mental model for entrepreneurs on how to approach FinTech products from the technical point of view.

So you want to build a stock trading app like Robinhood?
So you want to build a stock trading app like Robinhood?
  • Motivation — why I decided to write about building a FinTech product.
  • Market’s overview — existing companies and how different they are from each other.
  • Existing APIs — overview of the top API vendors.
  • Stock Exchange Data — how and where to get data to show to your users.
  • Real-time vs On-demand — on how it impacts your tech architecture and business model.
  • Business model — how to make money with your FinTech product.
  • Deposits and payouts — regulations and insurance aspects for…


A detailed guide on exporting Medium posts via Medium backup and republishing them on your Gatsby website.

How to clone your medium posts using custom Gatsby plugin
How to clone your medium posts using custom Gatsby plugin
How to clone your Medium posts using a custom Gatsby plugin

There’s a good ecosystem of plugins available on Gatsby’s website, and several of them address the functionality of getting your Medium posts to your Gatsby website. However, almost none of them allow you to copy the entire list of posts from your Medium account.

We will analyze existing solutions, and we will introduce a new plugin that does it efficiently.


An analysis of crypto-save random number generation on iOS and Android via JavaScript layer in React Native.

How to benchmark random number generation (RNG) in React Native
How to benchmark random number generation (RNG) in React Native
How to benchmark random number generation (RNG) in React Native

This article started as an effort to find a great UUID generation library. As a result, it led me to rewrite my existing react-native-uuid library in Typescript. However, I didn’t stop there. UUID generation is based on random number generation (RNG), which is an even bigger topic of Cryptography and specifically RNG.

If you don’t get your RNG right you risk having collisions between your UUIDs and your Encryption will be more vulnerable for statistical attacks.

RNBenchmark repo with all the code for RNG benchmarking.
react-native-benchmark library to run your benchmarks in React Native.


A step-by-step guide to building TypeScript wrapping around native code written using Objective-C and Kotlin.

How to build a react-native plugin in 2021
How to build a react-native plugin in 2021
How to build a react-native plugin in 2021

By design, react-native has a javascript executed in a single thread. Moreover, the react-native ecosystem is quite different from the node.js, which means packages like crypto are not available by default.

The goal of this tutorial is two-fold:

  • show how to generate crypto-safe random numbers in react-native;
  • show how to build and publish react-native plugin for both iOS and Android.
  1. Existing tools to build react-native plugins in 2021
  2. Pre-requirements
  3. Creating a library
  4. Building a TypeScript plugin interface with basic test coverage
  5. Building an Objective-C part


As you might know, an iOS application and its extensions use standalone data containers that do not intersect and can not be accessed from one another. This article outlines a technique for sharing data between the application itself and application extension bidirectionally. It uses NSUserDefaults configured with special suite via App Groups .

The final result of passing data from the React Native application to Action Extension
The final result of passing data from the React Native application to Action Extension

Submitting Trademark application via TEAS with USPTO

Reactive Lions Trademark
Reactive Lions Trademark
Reactive Lions Trademark

Do you want to register your name or your logo, or both? Of course, you can register a phrase or an image. Cases may vary significantly. In this article, we are covering how to register a trademark for a business name.

It will take less than 1 hour to apply, $250 per class. Use ™ sign when your application is pending. Use ® sign once USPTO confirms the registration of the trademark. Apply here.

Eugene Hauptmann

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