vault/ui/lib/core/addon/utils/common-prefix.js

export default function (arr = [], attribute = 'id') {
  if (!arr.length) {
    return '';
  }
  // this assumes an already sorted array
  // if the array is sorted, we want to compare the first and last
  // item in the array - if they share a prefix, all of the items do
  const firstString = arr[0][attribute];
  const lastString = arr[arr.length - 1][attribute];

  // the longest the shared prefix could be is the length of the match
  const targetLength = firstString.length;
  let prefixLength = 0;
  // walk the two strings, and if they match at the current length,
  // increment the prefixLength and try again
  while (
    prefixLength < targetLength &&
    firstString.charAt(prefixLength) === lastString.charAt(prefixLength)
  ) {
    prefixLength++;
  }
  // slice the prefix from the first item
  return firstString.substring(0, prefixLength);
}