Splunk Interview Question - Find first duplicate in sequence whose next value is the sum of its digits squared.

findFirstDuplicateInSeq.js

// i did poorly in my interview, the solution i gave worked but it was innefficient. 
// splunk passed on me, but i couldn't let it go. so here is my final solution of the problem
function findFirstDuplicateInSeq( _seq ) {
  const seq = [..._seq];// clone the array first so we are not mutating it.
  while(true){
    const next = seq[seq.length-1].toString().split('').map(v=>Math.pow(~~v,2)).reduce((a,b)=>a+b,0);// next val is sum of digits squared
    if(seq.indexOf(next)!==-1){
      return seq.length+1;// if seq contains our next value already, we found the first duplicate. return length+1
    }
    seq.push(next);// no match, push the next val in to the sequence
  }
}