2019:
React is lake a lot of utilities. But you don't need any npm package for that . just create somewhere the function classnames and call it when you need;
function classnames(obj){
return Object.entries(obj).filter( e => e[1] ).map( e=>e[0] ).join(' ');
}
or
function classnames(obj){
return Object.entries(obj).map( ([k,v]) => v?k:'' ).join(' ');
}
example
stateClass= {
foo:true,
bar:false,
pony:2
}
classnames(stateClass) // return 'foo pony'
<div className="foo bar {classnames(stateClass)}"> some content </div>
declare helper element and used it toggle method
(DOMToken?List)classList.toggle(class,condition)
example:
const classes = document.createElement('span').classList;
function classstate(obj){
for( let n in obj) classes.toggle(n,obj[n]);
return classes;
}