code: function getIndentation(str, index) {
    let indentStart = index;
    let indentEnd = index;
    while (indentStart) {
      const c = str.charCodeAt(indentStart - 1);
      // line break
      if (c === 10 || c === 13 || c === 0x2028 || c === 0x2029) {
        break;
      }
      indentStart--;
      // not white space
      if (c !== 9 && c !== 11 && c !== 12 && c !== 32 && c !== 160) {
        indentEnd = indentStart;
      }
    }
    return str.substring(indentStart, indentEnd);
  }
docs: Given a string and an index, look backwards to find the string of whitespace following the next previous line break.