function to get number need to be highlighted.

highlighter.js

// question at https://muhsalaa.com/journal/3ab005b6-2c66-4ccc-b7bb-df1be5ff8777

function highlight(nominal, uniqueCode) {
  // convert number to string
  const totalString = String(nominal + uniqueCode);
  const nominalString = String(nominal);
  let count = 0;
  
  // loop to count similar character by comparing nominal and total (nominal+unique code)
  for (let x = 0; x < totalString.length; x++) {
    if (nominalString[x] === totalString[x]) {
      count += 1;
    } else {
      // once it found different character, loop will break
      break;
    }
  }
  
  // finally, slice total amount with count, or number of same character
  // we will get the affected number by unique code addition
  return totalString.slice(count);
}