How to get a String from a variable depth in a javascript object

Question

i'm trying to get a string from a nested object, basically it's really simple. a server returns an error-code with a varying amount of --delimited strings (2-4) now basically what i want to do is

 return `${messageStrings[errorCodeParts[0]]
  [errorCodeParts[1]]
  [errorCodeParts[2]]
  [errorCodeParts[3]]}`

but only as far down as needed... (so 2 parts, do until errorCodeParts[1], 3 parts, do until errorCodeParts[2]. i don't know how to do this elegantly, can anyone point me in a direction?

this is the current code:

const messageStrings = {
  auth: {
    failed: 'These credentials do not match our records.',
    throttle: 'Too many login attempts. Please try again in :seconds seconds.',
  }
// ..
}

  getString(errorCode) {    // errorCode = 'auth-failed'
    const errorCodeParts = Array.from(errorCode.split('-'))

    let string = 'Unknown error'

        return `${messageStrings[errorCodeParts[0]]
  [errorCodeParts[1]]
  [errorCodeParts[2]]
  [errorCodeParts[3]]}` // but only those that are actually there
  }