Preview an image before it is uploaded

imgInp.onchange = evt => {
  const [file] = imgInp.files
  if (file) {
    blah.src = URL.createObjectURL(file)
  }
}

<form runat="server">
  <input accept="image/*" type="file" id="imgInp" />
  <img id="blah" src="#" alt="your image" />
</form>