js 字符串截取 slice 的小bug 以及处理方式

const str = '这里是荷逸啊';
console.log(str.slice(3,5));//荷逸

const str = '阿是𠮷娃娃🐱他说的纷';
console.log(str.slice(3, 6));//�娃娃

String.prototype.sliceByPoint = function (pStart, pEnd) {
  let result = ''; // 截取的结果
  let pIndex = 0; // 码点的指针
  let cIndex = 0; // 码元的指针
  while (true) {
    if (pIndex >= pEnd || cIndex >= this.length) {
      break;
    }
    const point = this.codePointAt(cIndex);
    if (pIndex >= pStart) {
      result += String.fromCodePoint(point);
    }
    pIndex++;
    cIndex += point > 0xffff ? 2 : 1;
  }
  return result;
};

  import 'sliceByPoint'
    const str = '阿是𠮷娃娃🐱他说的纷';
    console.log(str.sliceByPoint(3, 6));//娃娃🐱