画完一个多边形后，再画另一个多边形时，如何让前一个多边形消失

Question

  var Working=false;
  var points = [];
  var lastPoint = {x:0,y:0};
  var linArr = new Array();
 document.ondblclick=function ()
                      {
                         if(!Working) return;
                         var len = getLenth();
                         
                         var s='<v:line from="'+points[0].x+','+points[0].y+'" to="'+points[points.length-1].x+','+points[points.length-1].y+'" style="position:absolute;left:0px;top:0px;"></v:line>';
                         var o=document.createElement(s);
                         document.body.insertAdjacentElement('BeforeEnd',o);
   
                         
                         document.getElementById("show").innerHTML = "折线的总长度为：" + len + "px";
                         document.getElementById("show").style.display="";
                         points = [];
                         lastPoint  = {x:0,y:0}
                         Working=false;
 linArr.push(o);
                         }
  document.onmousedown=function ()
                        {
                       if(!Working)
                         {
 for (var i=linArr.length-1;i>=0 ;i--)
 {
document.body.removeChild(linArr[i]);
linArr.pop();
 }
                         document.getElementById("show").style.display="none";
                         Working=true;
                         lastPoint.x = event.x;
                         lastPoint.y = event.y;
                         points.push( {x:event.x,y:event.y} );
                         document.getElementById("show").innerHTML += "X:"+ lastPoint.x + " Y:" + lastPoint.y;
                         document.getElementById("show").style.display="";
                         }
                       else
                        {
                        var s='<v:line from="'+lastPoint.x+','+lastPoint.y+'" to="'+event.x+','+event.y+'" style="position:absolute;left:0px;top:0px;"></v:line>';
                                            
                        lastPoint.x = event.x;
                        lastPoint.y = event.y;
                        points.push( {x:event.x,y:event.y} );
                        document.getElementById("show").innerHTML += "<br/>X:"+ event.x + " Y:" + event.y;
                        document.getElementById("show").style.display="";
                        var o=document.createElement(s);
                        document.body.insertAdjacentElement('BeforeEnd',o);
 linArr.push(o);
                       }
                    }
  
  document.onmousemove=function ()
                       {
                       if(!Working) return;
                       }