It is very simple technique, define a function with very short name to return the object be using the above construct. This way we can reduce the page weight as well.
<script type="text/javascript">
function $(id)
{
return document.getElementById(id);
}
</script>
Use the $ function wherever you would like to get the object based on the id. $('x') would return the object reference of the page element which has the id "x".