<canvas?id="canvas">

</canvas>


<script>
???var?canvas?=??document.getElementById('canvas');
???var?context?=?canvas.getContext('2d');
???context.moveTo(100,100)//直線的起點(diǎn)

???context.lineTo(700,700)//直線的終點(diǎn)

???context.lineTo(100,700)//多筆畫時(shí)設(shè)置多終點(diǎn)即可

???context.lineTo(100,100)//最后的筆畫終點(diǎn)和開(kāi)始的起點(diǎn)同坐標(biāo)能連成一個(gè)完整形狀（每一筆都是以上一個(gè)終點(diǎn)為起點(diǎn)的）
???context.stroke();
</script>