Criar classes e usar no controller

Como criar classes para usar em um controller.

class UserController {
 Const document = new Document()
} 
module.exports = UserController
class Document {
 constructor(cpf) {
    if(cpf.length < 11){
      return false
    }
   return true
  }
}
module.exports = Document

Estou tentando assim mas está dando error no uso da class Document no controller UserController

// Class UserController

const Document = use('App/Helpers/Document')

class UserController {
  // You cannot create const variables inside class as class properties.
  // Use a constructor to define or initialise class properties.
  // Instantiate classes in class methods.
  // const document = new Document() //Wrong in the class block. Do this in a method.
  
  doSomethingMethod () {
    // Pass in cpf value into Document()
    const cpfValue = new Array(20)
    const document = new Document(cpfValue); // correct
    
    // Call isCpfValid method on the new instance of Document()
    const isValid = document.isCpfValid()
    console.log(isValid); // true

    // Or

    const isValid2 = document.getCpfValid
    console.log(isValid2); // true
    
  }
} 

module.exports = UserController

// Class Document
class Document {
 constructor(cpf) {
    this.cpf = cpf
  }

  isCpfValid () {
    if (this.cpf.length < 11) {
      return false;
    }
    return true;
  }
  
  /**
   * A getter. Call this method without executing it
   * That is: new Document(cpfValue).getCpfValid
   * Not: new Document(cpfValue).getCpfValid()
   */
  get getCpfValid () {
    if (this.cpf.length < 11) {
      return false;
    }
    return true;
  }
}

module.exports = Document

onde crio a classe, na controller mesmo