求帮看想在Html5中实现鼠标点击划线有什么问题

 <!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>划线</title>
<script language="javascript" type="text/javascript">
var c=document.getElementById("myCanvas");
var can=c.getContext("2d");

can.strokeStyle="rgb(0,182,0)";
var pois=new Array();
        can.lineWidth=2;
        mycanvas.onmousedown=function(e){
            can.clearRect(0,0,500,500);
            e=window.event||e;
            var sX=e.pageX-this.offsetLeft;
            var sY=e.pageY-this.offsetTop;
            var poi=Object.create({x:sX,y:sY});
            pois.push(poi);
            if(pois.length==1)
            {
                can.beginPath();
            }
            if(pois.length>1)
            {
                 can.moveTo(pois[0].x,pois[0].y);
                for(var i=1;i<pois.length;i++)
                {
                 can.lineTo(pois[i].x,pois[i].y);
                }
            can.stroke();
            }

}





你canvas对象都没放。。代码没有问题，除了mycanvas.onmousedown=function(e){....} 不能直接用id访问，改为c变量

 <canvas id="myCanvas"></canvas>
<script language="javascript" type="text/javascript">
var c=document.getElementById("myCanvas");
var can=c.getContext("2d");

can.strokeStyle="rgb(0,182,0)";
var pois=new Array();
        can.lineWidth=2;
        c.onmousedown=function(e){
            can.clearRect(0,0,500,500);
            e=window.event||e;
            var sX=e.pageX-this.offsetLeft;
            var sY=e.pageY-this.offsetTop;
            var poi=Object.create({x:sX,y:sY});
            pois.push(poi);
            if(pois.length==1)
            {
                can.beginPath();
            }
            if(pois.length>1)
            {
                 can.moveTo(pois[0].x,pois[0].y);
                for(var i=1;i<pois.length;i++)
                {
                 can.lineTo(pois[i].x,pois[i].y);
                }
            can.stroke();
            }

}

</script>

http://www.jb51.net/html5/95741.html

参考、。

查文档，canvas 文档多啊

mycanvas.onmousedown=function(e){....} 把mycanvas换成c试试