Why I cant choose content type when upload png image from javascript to minio

How can i upload an image from js to minio?

I tried this code.

minioClient.putObject('image-test', this.state.Img.name, this.state.result, 'image/png', function(err, etag) {
  if (err) return console.log(err)
  console.log('File uploaded successfully.')
});

i set content type as ‘image/png’ but on minio server i still got ‘binary/octet-stream’
enter image description here

and this is how I get file

 handleImageChange(e) {
  e.preventDefault();
  var reader = new FileReader();
  var file = e.target.files[0];
  reader.onloadend = () => {
  console.log('file name—',file);
  console.log('file result—',reader.result);
  this.setState({
    Img: file,
    result: reader.result
  });
 }
  reader.readAsDataURL(file)
}

the input component looks like

      <Button
        variant="contained"
        component="label"
        fullWidth
      >
        Upload File
        <input
          type="file"
          hidden
          onChange={e => this.handleImageChange(e)}
        />
      </Button>