Mutate object list values to object with values holding property paths

setPaths.js

/**
 * Convert
 *
 *   foo: {
 *     bar: ['baz', 'qux'],
 *   }
 *
 * to
 *
 *   foo: {
 *     bar: {
 *       baz: 'bar/baz/',
 *       qux: 'bar/qux/',
 *     }
 *   }
 */
function setPaths(obj, path = '', level = 0) {
  return Object.keys(obj).reduce((branches, key) =>
    !Array.isArray(obj[key]) ?
      {...branches, [key]: setPaths(
        obj[key],
        level === 0 ? path : (level === 1 ? key : [path, key].join('/')),
        level + 1
      )} :
      {...branches, [key]: {
        ...branches[key],
        ...obj[key].reduce((leaves, leaf) => ({
          ...leaves, [leaf]: [...path ? [path] : [], key, leaf].join('/') + '/',
        }), {}),
      }}
    , {}
  );
}