function containsEncodedComponents(x) {
  // ie ?,=,&,/ etc
  return (decodeURI(x) !== decodeURIComponent(x));
}

console.log(containsEncodedComponents('%3Fx%3Dtest')); // ?x=test
// expected output: true

console.log(containsEncodedComponents('%D1%88%D0%B5%D0%BB%D0%BB%D1%8B')); // шеллы
// expected output: false