你画好之后可能需要canvas 转成图片
const image = new Image()
// canvas.toDataURL 返回的是一串Base64编码的URL
image.src = canvas.toDataURL("image/png")
主要代码判断是电脑端还是手机端
if ('ontouchstart' in window) {
canvas.addEventListener('touchstart', onDrawStart);
canvas.addEventListener('touchmove', onDrawMove);
document.addEventListener('touchcancel',onDrawEnd);
document.addEventListener('touchend',onDrawEnd);
}else{
canvas.addEventListener('mousedown', onDrawStart);
canvas.addEventListener('mousemove', onDrawMove);
document.addEventListener('mouseup', onDrawEnd);
}