Passing values to a function and reading them

Hi All,
New user here.. I have a question on how to pass values to my javascript function.

I have this button:
<input type="button" value="Login" Onclick="DoLogin(this.value)"/>

But how would I pass the value of two other text fields instead of passing the value of the button? For instance If my form was:

<input type="text" name="username" />
<input type="password" name="password"/>
<input type="button" value="Login" Onclick="DoLogin(What do I put here?)"/>

And also, what about the function itself, currently it reads:

function DoLogin(str)

How should the function get these values Im passing in?

Thanks!

First we would need to see what the DoLogin() function actually contains. Post the javascript for that. We aren't psychic you know.

I figured it out .. if anyone is interested the code for the button would be:

Onclick="DoLogin(window.document.f1.username.value)"

f1 is the name of the form.

You don't need window there. That isn't what you originally asked either, you asked this
But how would I pass the value of two other text fields instead of passing the value of the button? For instance If my form was:
Had you asked about only one field then I could have told you that.