merge-class-names/dist/esm/index.js

A function that merges given class names, no matter their format: string with single or multiple class names or an array of class names. Filters out invalid class names as well.

export default function mergeClassNames() {
  return Array.prototype.slice.call(arguments).reduce(function (classList, arg) {
    return classList.concat(arg);
  }, []).filter(function (arg) {
    return typeof arg === 'string';
  }).join(' ');
}