const user = { name: 'Sarah', age: 28 };
const greeting = 'Hello';
const template = `${greeting}, ${user.name}! You are ${user.age} years old.`;

function createMessage(strings, ...values) {
  return strings.reduce((result, string, i) => {
    return result + string + (values[i] ? `[${values[i]}]` : '');
  }, '');
}

const tagged = createMessage`Welcome ${user.name}, age: ${user.age}!`;
console.log(template);
console.log(tagged);