title: How to extend a Joi schema?
body: <p>I have a joi schema called user</p>
  
  <pre><code>const user = {
    firstName: Joi.string()
      .min(2)
      .max(50)
      .required()
      .label('First Name'),
    lastName: Joi.string()
      .min(3)
      .max(50)
      .required()
      .label('Last Name'),
    email: Joi.string()
      .allow('')
      .email({ minDomainAtoms: 2 })
      .max(100)
      .label('Email Address'),
  }
  </code></pre>
  
  <p>I had another one called owner</p>
  
  <pre><code>const ownerSchema = {
    firstName: Joi.string()
      .min(2)
      .max(50)
      .required()
      .label('First Name'),
    lastName: Joi.string()
      .min(3)
      .max(50)
      .required()
      .label('Last Name'),
    email: Joi.string()
      .allow('')
      .email({ minDomainAtoms: 2 })
      .max(100)
      .label('Email Address'),
    number: Joi.string()
      .regex(/[0-9]/)
      .length(10)
      .required()
      .label('Phone Number'),
    dateOfBirth: Joi.date(),
  
    kycDetails: Joi.array()
      .items(schemaKyc)
      .required(),
    bankDetails: Joi.array()
      .items(schemaBank)
      .required(),
    licenceDetails: Joi.array()
      .items(schemaLicence)
      .required(),
    insuranceDetails: Joi.array()
      .items(schemaInsurance)
      .required()
  };
  </code></pre>
  
  <p>As you can see the both have three fields in common I want to be able to use the user schema in owner and whenever I make changes to the user I want it to reflect in the owner as well.</p>