example-layering-with-validate-body.js

/*

Here's a bit of code demonstrating the cascade of usign `static` functions within a class. 
From top to bottom each subsiquent function utilizes the next. This allows you to piece-meal 
the functions needed by declaring the method names based on what they return i.e. `bool`, `throw`, and `middleware`.
Note, I'm intentionally not using a constructor here, and I am also intentionally passing in 
the same arguments to each of the function methods.

*/

class ValidateBody {
  static errorMessage = 'invalid body'
  static errorCode = '123'
  static Error = Error
  static bool (body) {
    if (!body) return false
    if (!body.header) return false
    if (!body.header.data) return false
    return true
  }
  static error (body) {
    if (!ValidateBody.bool(body)) {
      return new ValidateBody.Error(`${ValidateBody.errorCode}: ${ValidateBody.errorMessage}`)
    }
    return null
  }
  static throw (body) {
    const result = ValidateBody.error(body)
    if (result instanceof Error) {
      throw ValidateBody.error(body)
    }
    return null
  }
  static middleware () {
    return (req, res, next) => {
      return next(ValidateBody.thrower(req.body))
    }
  }
}

console.log(ValidateBody.bool({}))
console.log(ValidateBody.throw({}))
console.log(ValidateBody.middleware({})())