How to extend error when prepending a message to an existing error which may or may not be instance of Error

extending-error.js

function showDeep(t){
    let o=t
    do {
      console.log(`--- ${o.constructor.name}`)
      for (let k of Reflect.ownKeys(o)) {
        let d = Reflect.getOwnPropertyDescriptor(o,k)
        if (JSON.stringify(d.value)!==undefined) {
          console.log(`${k} : ${JSON.stringify(d.value)}`)
          if (k==='stack')
            console.log("") // funky
        }
      }
    } while (o=Reflect.getPrototypeOf(o))
  }
  
  class X extends Error {
    constructor(m,e=null) {
      let prev_stack=null
      let msg = m
      if (e instanceof Error) {
          msg += ", " + e.message
          prev_stack=e.stack
      } else { 
        if (e && JSON.stringify(e)!==undefined) { 
          msg += ", " + JSON.stringify(e)
        }
      }
      super(msg)
      // her do something e.stack and this.stack if desired
      if (prev_stack)
          this.stack += '\n' + prev_stack
      this.name=this.constructor.name
    }
  }
  class Y extends X {
    constructor(m,e){
      super(m,e)
    }
  }
  console.log("~~~~~~~~~~~~~~~~~~~~ new Error('help')")
  let e = new Error('help')
  //e.stack="original e stack" // this will be lost
  showDeep(e)
  console.log("~~~~~~~~~~~~~~~~~~~~ new Y('y')")
  let y = new Y("y")
  showDeep(y)
  console.log("~~~~~~~~~~~~~~~~~~~~ new Y('y',e)")
  let ye = new Y("y",e)
  showDeep(ye)