点与线的距离及垂足点

<html>
<head>
<meta http-equiv="Content-Type" content="text/html">
<title>点与线的距离及垂足点</title>
</head>

<script language=javascript>
	function dist(x, y, startx, starty, endx, endy)
	{
		var se =  (startx-endx)*(startx-endx)+(starty-endy)*(starty-endy);//线段两点距离平方
		var p = ((x-startx)*(endx-startx)+(y-starty)*(endy-starty)); //向量点乘=|a|*|b|*cosA
		var r = p/se; //r即点到线段的投影长度与线段长度比
		var outx=startx+r*(endx-startx); 
 		var outy=starty+r*(endy-starty); 
  	var des =(x-outx)*(x-outx)+(y-outy)*(y-outy);
		alert(outx);
		alert(outy);
		alert(Math.round(Math.sqrt(des)));
	}
</script>
<body>
	<input type=button value='dist' onclick="dist()">
<textarea id='textjs' rows="20" cols="120">
dist(5,20,1,6,20,15);
</textarea>
<br>
<input type="button" value="run javacript" onclick="javascript:eval(textjs.value);">
</body>
<html>