how to show/hide buttons??

[tpravioti]

hi there!!
i am making a gallery with chekboxes and i want to hide both buttons(with ids:'btn_next' and 'btn_prev') when i have less than my offset number but i can't make it..what i need to change in this code?it hides and shows my buttons only when i have more images than the offset..i call this function with 'changestep(0);'

here is my code:

var step=0;
var offset=6;

function changestep(st)
{
	var len=images.length;
	var maxsets=parseInt(len/offset);
	
	if (st==0) {
		step=0;
		maxsets=1;
		update_tag();
	}
	else {
		step=step+st;
		if (step>maxsets) {
			step=maxsets-1;
		}
		update_tag();
	}
	
	//buttons display or not
	if (step == 0) {
		$('btn_prev').style.visibility='hidden';
	} 
	else {
		if (step == (maxsets-1)) {
			$('btn_next').style.visibility='hidden';
			$('btn_prev').style.visibility='visible';
		}
		else {
			$('btn_prev').style.visibility='visible';
			$('btn_next').style.visibility='visible';
		}
	}
	
//alert('len:'+len+' offset:'+offset+' maxsets:'+maxsets+' step:'+step+' st:'+st);
}

please help me as fast as you can!!thanks!!