javascript - 如何更改外部函数参数

Question

我有一个程序可以查看两个点并对它们进行操作。不过，我需要始终确保这些点的顺序正确。我需要第一个点是两者中较小的一个。我正在尝试编写一个实用程序函数，我可以在其他函数内部调用它来重新排序传入的参数。任何有助于理解为什么这不起作用的帮助都会很棒!我会尽力只发布相关代码

var unionFind = {
  data: [],     //This will be filled by a later function
  reorderPoints: function(num1, num2) {
    // useful utility to make sure points are in proper order
    // we will always keep the smaller number to show if points
    // are connected.
    if(num1 > num2) {
      debugger;
      point1 = num2;
      point2 = num1;
    }
  },
  union: function(point1, point2) {
    this.reorderPoints(point1, point2);
    // if the two points are already connected
    // then just return true
    if(this.connected(point1, point2) === true) {
      return true;
    }
    // otherwise loop through the data array and
    // change all entries that are connected to
    // the first point to the value of the first
    // point
    for(var i = 0; i < this.data.length; i++) {
      if(this.data[i] === point2) {
        this.data[i] = point1;
      }
    }
  },

  connected: function() {
    this.reorderPoints(point1, point2);
    return this.data[point1] === this.data[point2];
  },
  initData: function(num) {
    for(var i = 0; i <= num; i++) {
      this.data[i] = i;
    }
  }
};

unionFind.initData(9);
console.log(unionFind.data);

unionFind.union(4,3);
console.log(unionFind.data);

Answer 1

在union方法中，point1和point2是参数，所以是局部变量。当您输入 reorderPoints 方法时，它们在那里不存在，因此此代码:

point1 = num2;
point2 = num1;

只是创建新的 point1 和 point2 变量(这次是全局变量，因为之前没有 var)。

要解决这个问题，您需要在这两个函数之外的命名空间中声明 point1 和 point2 变量，或者您可以构建这两个点的数组并将其传递数组到排序方法，像这样:

  reorderPoints: function(points) {
    if(points[0] > points[1]) {
      var tmp = points[0];
      points[0] = points[1];
      points[1] = tmp;
    }
  },
  union: function(point1, point2) {
    var points = [point1, point2];
    this.reorderPoints(points);
    // From this line you should use points[0] and points[1] as sorted points
    // because point1 and point2 parameters are not changed.
    (....)