It comprises 3 parts:
Back in the late 90's web developers had to be versed in the quirks of each browser. It was a frustrating time, but thankfully things have evolved over the years. Since HTML5, we can revel in the security that our HTML/CSS/JS code will work equally well in all the different browsers (mostly... most of the time!)
But now we have a new challenge: different mobile app platforms. We have iOS, Android and Windows, which require Objective-C, Java, and C#... and that's just for starters. We also need awareness of the different user experience on each platform.
Enter React Native, a project started by Facebook and used in the Facebook app, Instagram, AirBnb and Wix. It's a Javascript layer over the native modules in iOS and Android. Javascript gets compiled into native code for each platform.
It borrows heavily from React, a javascript view layer for the browser, which allows for composable components.
And that's all very exciting!
While the app is simplistic, it demonstrates that Web and Mobile are converging. I believe that React Native can take us 80% of the way towards a proper native mobile experience... and that's a long way.
Equally, Javascript (the love-it-hate-it programming language) can be used on the entire stack - in the database, the JSON data, the browser, and mobile. Full stack developers rejoice!