JS File
    <input type="file" name="inputfile"
            id="inputfile">
    <br>
   
    <pre id="output"></pre>

<script type="text/javascript">
        document.getElementById('inputfile').addEventListener('change', function() {
              var plik =  document.getElementById('inputfile');
			
            var fr=new FileReader();
            fr.onload=function(){
                document.getElementById('output')
                        .textContent=fr.result;
            }
              
            fr.readAsText(this.files[0]);
        })
    </script>