图片转画布

function blobToImg (blob) {
  return new Promise((resolve, reject) => {
    let reader = new FileReader()
    reader.addEventListener('load', () => {
      let img = new Image()
      img.src = reader.result
      img.addEventListener('load', () => resolve(img))
    })
    reader.readAsDataURL(blob)
  })
}
  function  ImageToCanvas(image,dom) {
      const canvas = document.getElementById(dom)
      canvas.width = image.width
      canvas.height = image.height
      canvas.getContext('2d').drawImage(image, 0, 0)// 0, 0参数画布上的坐标点，图片将会拷贝到这个地方
      return canvas
  }