Separate HTML, CSS, and JavaScript source code each into its own file.  You can name these files
index.htm, styles.css, and 
script.js. Even this statement violates the separation 
of HTML and JavaScript source code:
<button id="btn1" onclick="convert( );">
    Convert
</button>
Instead of onclick="convert( );" in your HTML file, use 
the following JavaScript code in your JS script instead:
function init( ) {
    var button = document.getElementById("btn1");
    button.addEventListener("click", convert);
}
window.addEventListener("load", init);
30% penalty if HTML, CSS, and JS source code is not separated into separate files.