javascript 画带箭头的线段

function drawArrow(x0,y0,x1,y1){
var d=Math.sqrt((y1-y0)*(y1-y0)+(x1-x0)*(x1-x0));
var Xa = x1 + 10 * ((x0 - x1) + (y0 - y1) / 2) / d;
var Ya = y1 + 10 * ((y0 - y1) - (x0 - x1) / 2) / d;
var Xb = x1 + 10 * ((x0 - x1) - (y0 - y1) / 2) / d;
var Yb = y1 + 10 * ((y0 - y1) + (x0 - x1) / 2) / d;
var html="<v:polyline style='Z-INDEX:1;LEFT:0;POSITION:absolute;TOP:0' points='"+x0+","+y0+","+x1+","+y1+","+Xa+","+Ya+","+x1+","+y1+","+Xb+","+Yb+"' filled='f' />";
//pl.points.value=x0+","+y0+","+x1+","+y1+","+Xa+","+Ya+","+x1+","+y1+","+Xb+","+Yb;
container.innerHTML+=html;
}