Learn once, write anywhere
Motivation to stick with it
I picked up ruby language in 2008 and I fell in love with it. The philosophy was "Programming languages must feel natural to programmers." instead of hammering my head to figure out how to write codes in proper way. And that sparked various open source projects. I see the similar thing is happening in JS community. Lots of mobile devs are suffering because of iOS / Angular. React Native is trying to tackle that problem.
It's worth noting that we're not chasing “write once, run anywhere.” Different platforms have different looks, feels, and capabilities, and as such, we should still be developing discrete apps for each platform, but the same set of engineers should be able to build applications for whatever platform they choose, without needing to learn a fundamentally different set of technologies for each. We call this approach “learn once, write anywhere.” — Tom Occhino, "React Native: Bringing modern web techniques to mobile", Facebook Code Blog, (Mar. 26, 2015)
It's expanding beyond web and mobile. VR is the next thing they are working on now.