FIle.WriteAllText not adding text

I have html/javascript code that I am trying to write in c sharp on a windows forms application. It looks like this

<html>
<body>
<button onclick = "Clicker()">Click Me </button>
<script src = "clicker.js"></script>
</body>
</html>

here is what clicker.js looks like


function Clicker(){
    document.body.innerHtml += "adding to document";
}

I was able to setup the onclick event in c sharp, but when I click the button, the file that I am writing to is not continuing to add “adding to document” to the document. It only does it once. Here is what the event looks like

void ButtonClick(object k, EventArgs e){
   File.WriteAllText(location,"adding to document");
}

Why is this not working?