Where JQuery was once a necessity for building complex dynamic crossbrowser web pages, on today's browsers the popular parts of JQuery mostly just make the syntax sightly shorter and fix tiny inconsistencies.

JQuery functionality is for the largest part integrated in modern browsers, JQuery is living on because of momentum, it's ecosystem and the desire to support older browsers.

React meanwhile is popular in some places, but hasn't reached nearly the age and ubiquity that would warrant a native browser implementation.