User.js

class User {
  constructor({ name, age }) {
    this.name = name;
    this.age = age;
  }

  validate() {
    const hasName = Boolean(this.name);
    const hasMinAge = this.age >= User.MIN_AGE;

    const validation = {
      isValid: hasName && hasMinAge
    };

    if(!hasName) {
      validation.error = {
        name: 'Name is empty'
      };
    }

    if(!hasMinAge) {
      validation.error = validation.error || {};
      validation.error.age = 'Age is not the  minimum';
    }

    return validation;
  }
}

User.MIN_AGE = 18;

module.exports = User;