React had 2 major contributions which were industry changing on the front end, IMO, and may not have happened or would have happened a lot later without it.

1. Virtual Dom 2. One way data binding

I think one could argue that the virtual DOM wasn’t important, and possibly even led the industry in the wrong direction considering how it’s not as popular, for good reasons, anymore.

One way data binding was huge, however. Every other framework at the time was proudly promoting 2 way data binding. 2 way data binding would be in their website’s hero image and their entire sample app (invariably a todo list app) would be based around promoting the benefits of 2 way data binding.

I think minus React, a switch to one way data binding would have taken much longer, simply because the momentum behind 2 way data binding was so strong.