画布基本功能——导出图画

将canvas的图通过canvas.toDataURL(MIMEType: String)导出

const canvas = document.getElementById('canvas')
if(canvas.getCOntext) {  //确保浏览器支持canvas
  let imageURI = canvas.toDataURL("image/png")  //传入canvas图画导出后的文件类型
  let image = document.createElement("img")
  image.src = imageURI
  document.body.appendChild(image)
}

上述的imageURI是base64字符串，形如：data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAMgAAADICAYAAA....