Hi Guys,

I am new at JavaScript and start to do some tutorials.What I am trying to do here is prompting user to input a name and if the name was valid the page(document) will display with all objects like the button.But if user enter a wrong name then the button will be disabled!
I create the following code but it did not work

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>New Web Project</title>
<script language="JavaScript" type="">
function changeColor(){
document.bgColor = "Gray";
<script language="JavaScript" type="text/javascript">
var person = "";
person = prompt('What is Your Name:');
if (person == "Foo") {
document.write("<h1 />Welcome " + person);
document.bgColor = "Yellow";
else {
document.write("<h1 />Access Denied!!!!");
document.bgColor = "Red";
document.getElementById("gree").disabled = true;

<p/><input id="gree" type="button" value="Gray " onClick="changeColor();">

as you can see I used the:
document.getElementById("gree").disabled = true;
but it did not work , could you please give an idea how I can solve this problem?