magic array change

function joinArrayRange(array, start, end, color, normalize) {
  let result = '';
  const joined = array.slice(start, end + 1).join(' ');
  array.splice(start, end - start + 1, `<span style="background: ${color}">${joined}</span>`, ...[...Array(end - start).fill('<xxx>')]);
  if (normalize) {
    result = array.filter(item => item !== '<xxx>').join(' ');
  } else {
    result = array.join(' ');
  }

  return result;
}

function getWordsCoordinate(words, start, end) {
	const targetIndex = words.slice(0, start).trim().split(' ').length;
  const numberOfWord = word.slice(start, end).trim().split(' ').length
  return [targetIndex, targetIndex + numberOfWord - 1 ];
}

function replaceWordByCoordinateUnreliable(foo, coord) {
  let words = foo
  const changed = [];
  for (let index of coord) {
    const id = makeid(index[1] - index[0] + 1)
  	const target = words.substring(index[0], index[1] + 1);
    changed.push({ id, content: `<spans>${target}</spans>`});
    words = words.substring(0, index[0]) 
  		+ id 
  		+ words.substring(index[1] + 1, words.length)
  }
  
  console.log(words)
  
  for (let item of changed) {
  	words = words.replace(item.id, item.content);
  }
  
  return words;
}