Do I want to know why my script is not taken the id value?

I used this code in a separate folder in a single file that was named by test.js
this is my starting code.

var myInput = document.getElementById(newPass);

var confInput = document.getElementById(confpsw);

var letter = document.getElementById(letter);

var capital = document.getElementById(capital);

var number = document.getElementById(number);

var length = document.getElementById(length);

var special = document.getElementById(special);    

document.getElementById(Button).disabled = true;

my view code is..

<button id=Button class=btn btn-lg btn-primary btn-block btn-signin type=submit>Submit</button>

I got the error like this...

Uncaught TypeError: Cannot set property 'disabled' of null

why my script is not working in cshtml?