Display content

I am completely new to this json
I would like to display a file content in a dialog box. any idea please.

something like

Code:

---

function onLoad(obj){
    alert(obj.reponseText)
}
//Create a button to press for fun
    <input type="button" onclick="sendRequest(onLoad,' ', 'GET', '[yourfilename]', true, true)">

---

Best regards,