function ProtoError (code) {
  const error={
    "1":{
      "code": 100,
      "text": "foo"
    },
   ///...
  }
  self=this
  return error[code]
 }
ProtoError.prototype.fullText = function(){
  return this.code+" "+this.text
}

a = new ProtoError(100) //
console.log(a) // { code: 100,  text: 'foo'}
b=a.fullText() //a.fullText is not a function

{
  "code": 100,
  "text": "foo"
}