TypeScript选择排序类连续调用双排序方法失效问题求助

我学习了简单的选择排序（selection sort）算法并尝试用JavaScript/TypeScript实现。以下是我的SelectionSort类代码：

export default class SelectionSort {
  private dataForSmallestToBiggest: number[];
  private dataForBiggestToSmallest: number[];
  public startData: number[];
  private biggestIndex: number = 0;
  private biggest: number = 0;
  private smallestIndex: number = 0;
  private smallest: number = 0;
  public iterationSmallestToBiggest: number = 0;
  public iterationBiggestToSmallest: number = 0;

  constructor(data: number[]) {
    // initiate for array smallest to biggest
    this.dataForSmallestToBiggest = data;
    // initiate for array biggest to smallest
    this.dataForBiggestToSmallest = data;
    // initiate for start data
    this.startData = data;
  }

  // set biggest data
  private setBiggest() {
    // initiate biggest data
    this.biggest = this.dataForBiggestToSmallest[0];
    //initiate biggest index data
    this.biggestIndex = 0;
    // looping for searching biggest index and biggest value from array
    this.dataForBiggestToSmallest.forEach((val, index) => {
      // if biggest found
      if (val > this.biggest) {
        // change biggest value
        this.biggest = val;
        // change biggest index
        this.biggestIndex = index;
      }
      // increase how many iteration for this looping
      this.iterationBiggestToSmallest++;
    });
  }

  // searching smallest data
  private setSmallest() {
    // initiate smallest data
    this.smallest = this.dataForSmallestToBiggest[0];
    //initiate smallest index data
    this.smallestIndex = 0;
    // looping for searching smallest index and smallest value from array
    this.dataForSmallestToBiggest.forEach((val, index) => {
      // if smallest found
      if (val < this.smallest) {
        // change the smallest value
        this.smallest = val;
        // change the smallest index
        this.smallestIndex = index;
      }
      // increase how many iteration for this looping
      this.iterationSmallestToBiggest++;
    });
  }
  // sorting from smallest to biggest
  public smallestToBiggest() {
    // initiate result variable
    let result: number[] = [];

    while (this.dataForSmallestToBiggest.length > 0) {
      //  change smallest value and smallest index
      this.setSmallest();
      // add result from smallest data;
      result.push(this.smallest);

      // remove array  by smallest inex
      this.dataForSmallestToBiggest.splice(this.smallestIndex, 1);
      // increase how many sorting smallest to biggest sort
      this.iterationSmallestToBiggest++;
    }
    return result;
  }

  // sorting from biggest to smallest
  public biggestToSmallest() {
    // initiate result variable
    let result: number[] = [];
    while (this.dataForBiggestToSmallest.length > 0) {
      //  change biggest value and biggest index
      this.setBiggest();

      // add result
      result.push(this.biggest);
      // remove array  by biggest inex
      this.dataForBiggestToSmallest.splice(this.biggestIndex, 1);
      // increase how many sorting smallest to biggest sort
      this.iterationBiggestToSmallest++;
    }
    return result;
  }
}

单独调用biggestToSmallest或smallestToBiggest方法时，排序功能均正常。但同时调用两个方法时，仅biggestToSmallest生效，smallestToBiggest无结果输出，且startData属性也被清空。请问我的代码哪里出错了？为何仅第一个方法有效？

问题根源 #

JavaScript/TypeScript中数组是引用类型，你在构造函数里直接将传入的data数组赋值给三个类属性，这意味着三个变量实际上指向内存中的同一个数组。当你调用任意一个排序方法时，方法内部通过splice()修改数组（删除元素），会直接改变这个共享的原数组。

比如先调用biggestToSmallest，方法会循环删除数组元素直到为空，此时dataForSmallestToBiggest和startData指向的也是这个空数组，后续调用smallestToBiggest时，循环条件this.dataForSmallestToBiggest.length > 0不成立，直接返回空数组。

修复方案 #

在构造函数中为每个属性创建独立的数组副本，避免引用共享。对于纯数字数组，使用扩展运算符[...data]或data.slice()即可实现浅拷贝：

constructor(data: number[]) {
  // 创建独立数组副本，避免相互影响
  this.dataForSmallestToBiggest = [...data];
  this.dataForBiggestToSmallest = [...data];
  this.startData = [...data];
}

修改后，每个排序方法操作的都是自己专属的数组副本，调用顺序不再影响结果，startData也会始终保留初始的数组值。

内容的提问来源于stack exchange，提问作者Al Youma Akmal