I know how to access an element by itīs id, but how could I get the id of an element

Letīs say I have

Code JavaScript:
var id;
function getid()
var get=get the id of the element that triggered the function;
<input type="submit" id="test" onclick="getid()">

this is the code I have, but I want to use it for different fields, it works right now, but if the first change to the fields is made on field4 then the script will not work, I found a way around and made it work in my form but I am looking for a way to get the id of an element so I dont have to be looking for "ways around" in the future and also to make my code smaller.

Does anyone know how I can retrieve the id of an element on a onchange or other event?

Code HTML4Strict:
<script type="text/javascript">
var x=1;
var ids="test";
function fixuplow()
var myvar=(document.getElementById(ids+x).value);
var process=(myvar.toLowerCase());
var final=(process.charAt(0).toUpperCase() + process.slice(1));
something to up and lower case: <input type="input" id="test" onchange="fixuplow()">

thanks for your help!!!!!