document.getElementById isn't working

[risk32]

Hi all. I'm not exactly sure what I'm doing wrong, but when I try to use the document.getElementById() method, it's not working. Here's what I have:

var username = document.getElementById('username')
 
function test()
    {
        document.write(username)
    }
 
...
 
Username: <input type="text" id="username">
<input type="button" value="test" onClick="test();">
 

(I am aware that I don't use braces in standard format, it just helps me keep track of what I'm doing)

When I click the button, the only thing it returns is null. Am I doing something wrong?

[Dormilich]

yes and no. if you call getElementById() before the document tree is finished (resp. the element in questions is attached to the DOM) you get null as result.

[risk32]

@Dormilich
Where would be the appropiate location for the document.getElementById() method?

[risk32]

I actually feel like an idiot. Even though the variable was assigned globally, it didn't read inside the function. So, I put it inside the function and added .value to the end for the alert. It's working. Now to figure out arrays...