javascript实现函数重载的深入探索

<script>
function Point2D(x, y)
{
 this.x = x;
 this.y = y;
 Point2D.prototype.quadrant = function()
 {
  if (x > 0 && y > 0) return "I";
  else if (x < 0 && y > 0) return "II";
  else if (x < 0 && y < 0) return "III";
  else if (x > 0 && y < 0) return "IV";
  else if (x == 0) return "x-axis";
  else if (y == 0) return "y-axis";
  else throw new Error();
 }
 Point2D.prototype.toVector = function()
 {
  return new Vector2D(x, y);
 }
 Point2D.prototype.distance = function() //求距离
 {
  if (arguments.length == 1 && arguments[0] instanceof Point2D)
  {
   return this._point_distance.apply(this, arguments);
  }
  else if (arguments.length == 1 && arguments[0] instanceof Vector2D)
  {
   return this._vector_distance.apply(this, arguments);
  }
  else
  {
   throw new Error("Argument Error!");
  }
 }
 Point2D.prototype._point_distance = function(p)  //求两点之间的距离(函数重载)
 {
  return (new Vector2D(p,this)).length();
 }
 Point2D.prototype._vector_distance = function(v)  //求点到向量的距离(函数重载)
 {
  var v1 = new Vector2D(this, v.start);
  var v2 = new Vector2D(this, v.end);

  var area = Math.abs(v1.cross(v2));  //平行四边形面积 = v1 X v2 = |v1v2|sin(v1,v2)
 
  return area / v.length();   //平行四边形面积除以底边长度即为点到向量的距离
 }
}
function Vector2D()
{
 if (arguments.length == 2 && arguments[0] instanceof Point2D && arguments[1] instanceof Point2D)
 {
  _point_point_Vector2D.apply(this, arguments);
 }
 else if (arguments.length == 2 && !isNaN(arguments[0]) && !isNaN(arguments[1]))
 {
  _double_double_Vector2D.apply(this, arguments);
 }
 else if (arguments.length == 4 && !isNaN(arguments[0]) && !isNaN(arguments[1])
  && !isNaN(arguments[2]) && !isNaN(arguments[3]))
 {
  _double_double_double_double_Vector2D.apply(this, arguments);
 }
 else
 {
  throw new Error("Argument Error!");
 }
}
function _point_point_Vector2D(p1, p2)  
{
 this.start = p1;
 this.end = p2;
 Vector2D.prototype.length = function() //求向量的长度
 {
  return Math.sqrt(this.pond_x() * this.pond_x() + this.pond_y() * this.pond_y());
 }
 Vector2D.prototype.pond_x = function() //x方向分量
 {
  return this.start.x - this.end.x;
 }
 Vector2D.prototype.pond_y = function()
 {
  return this.start.y - this.end.y;
 }
 Vector2D.prototype.cross = function(v)   //求向量的交积 P1 X P2 = x1y2 - x2y1
 {
  return this.pond_x() * v.pond_y() - v.pond_x() * this.pond_y();
 }
}
function _double_double_Vector2D(x,y) //重载构造函数Vector2D
{
 this.pointPairs = new Array();
 this.pointPairs[0] = new Point2D(0, 0);
 this.pointPairs[1] = new Point2D(x, y);

 _point_point_Vector2D.apply(this, this.pointPairs);
}
function _double_double_double_double_Vector2D(x1, y1, x2, y2)  //重载构造函数Vector2D
{
 this.pointPairs = new Array();
 this.pointPairs[0] = new Point2D(x1, y1);
 this.pointPairs[1] = new Point2D(x2, y2);

 _point_point_Vector2D.apply(this, this.pointPairs);
}
var p1 = new Point2D(0,0);
var p2 = new Point2D(10,10);
var v1 = new Vector2D(p1,p2);  //通过两个点(p1,p2)的方式来构造向量V1
alert("向量v1长度:"+v1.length());
var v2 = new Vector2D(0,0,5,5);  //通过四个坐标(x1,y1,x2,y2)的方式来构造向量V2
alert("向量v2长度:"+v2.length());
var v3 = new Vector2D(0,10);  //通过指定终点的方式来构造向量V3
alert("向量v3长度:"+v3.length());
alert("向量v1与v2的交积:"+v1.cross(v2));  //求V1 X V2 (因为平行，所以结果为0)

var p3 = new Point2D(10,0);
alert("点p1与p3的距离:"+p1.distance(p3));
alert("点p3与向量v1的距离:"+p3.distance(v1));
</script>