how to upload an image dynamically using javascript

HTML:

<div id='clock'></div>
<input type='file' id='getval' /><br/><br/>

CSS:

#clock{

    background-image:url('');

    background-size:cover;

    background-position: center;

    height: 250px; width: 250px;

    border: 1px solid #bbb;

}

JS:

document.getElementById('getval').addEventListener('change', readURL, true);

function readURL(){

    var file = document.getElementById("getval").files[0];

    var reader = new FileReader();

    reader.onloadend = function(){

        document.getElementById('clock').style.backgroundImage = "url(" + reader.result + ")";        

    }

    if(file){

        reader.readAsDataURL(file);

    }else{

    }

}