Recs.
Updated
SpecsUpdate
Pros
Pro Virtual DOM support
Instead of relying on the DOM, React implements a virtual DOM from scratch, allowing it to calculate precisely what needs to be patched during the next screen refresh. This is orders of magnitude faster than fiddling with the DOM itself.
Pro Good debugging tools
React has an official Chrome Extension which is used as a developing and debugging tool. It can be used to quickly and painlessly debug your application or view the whole application structure as it's rendered.
Pro Quick
React very quickly updates its components thanks to the virtual DOM. It only updates what needs to be updated.
Pro Synthetic Events
DOM differences and spec inconsistencies are abstracted away. Bubbling works correctly. onChange fires onChange since that's what you'd expect (vs reality where some browsers that don't fire the change handler onBlur for some inputs). You also get top level events for free. You can declare your intention and React will figure out the optimal way to attach event handlers.
Pro Flux architecture pattern
Flux is a platform agnostic pattern which can technically be used with any application or programming language.
One of Flux' main features is that it enforces uni-directional data flow which means that views do not change the data directly.
With React this is useful because this way it's easier to understand an application as it starts getting more complicated. By having two-way data binding, lead to unpredictable changes, where changing one model's data would end up updating another model. By using the Flux architecture, this can be avoided.
Cons
Con Not a complete solution
React does not do everything for the developer, it's merely a tool for building the UI of a web app. It does not have support for routing or models, at least not out of the box. While some missing features can be added through libraries, to start using React and use it in production, you still would need to have experience, or at least a good grasp on what the best libraries to use would be.
Con You have to learn a new syntax
Requires to learn a custom syntax, JSX that has some gotchas and introduce complexity, a steeper learning curve, and incompatibility with other tools.
Though you can opt out from JSX and use vanilla JS instead. But that is not recommended since it adds a lot of unneeded complexity which JSX tries to avoid.
Con Large file size
React's react.min.js
is 145.5KB in size. It's much larger than some other libraries that offer roughly the same features and it's almost the same size as some MV* frameworks such as Angular or Ember that offer more features out of the box.
Although, it should be mentioned that sometimes having a smaller library may force developers to reinvent the wheel and write inefficient implementations on features that React already has. Ending up with a larger application that's harder to maintain and/or that has bad performance.
Recommendations
Comments
Flagged Pros + Cons
Con Some issues with DOM manipulation libraries are possible (e.g., jQuery)
Out of Date Pros + Cons
Con Patents license
The problem with React is its patent rider. React.js comes with a BSD license, but has a patent rider that gives you a license to React's patents. This sounds like a good thing, right? But this rider has a "strong retaliation clause" which says that if you make any sort of patent claim against Facebook, this patent license automatically terminates. This means Facebook can now sue you for patent infringement for using React. While you may think this is no worse than not having a patent rider at all, but that's not the case. If there is no patent rider, then there is an implicit grant which cannot be revoked.
If you work for a software company and your company has patents then keep in mind that by using React you are giving Facebook a free license to your entire patent portfolio.
More info on weak vs strong retaliation clauses.