I think around React 0.14, they announced that React's support for es6 class syntax wouldn't support mixins, and you'd only be able to get them by using the old

I think around React 0.14, they announced that React's support for es6 class syntax wouldn't support mixins, and you'd only be able to get them by using the old .createClass method. I think they pointed out that they didn't see this as a big issue because mixins were a pattern they wanted to get away from anyway and saw better solutions to.