Working with the DOM API is hard. React basically gives developers the ability to work with a virtual browser that is faster and more friendly than the real browser. React’s virtual browser acts like an agent between the developer and the real browser.
The Skype team at Microsoft are happy to announce that they are open sourcing ReactXP, a library that we developed for cross-platform development. It builds upon React JS and React Native, allowing you to create apps that span both web and native with a single code base.
When you download slack you're actually downloading a complete copy of Google Chrome. Chrome, at the time of writing is 15 million non-comment lines. When you download slack, 99% of the code is 'below the water'.