function _(str){
	if(typeof(str)!='object') return document.getElementById(str);
	else return str;
}

function initNavigation(){
	var domEle = _('mainNav');
	var arrIMG = domEle.getElementsByTagName('img');
	for(var k in arrIMG){
		if(typeof(arrIMG[k])=='object'){
			if(arrIMG[k].getAttribute('class')=='off' || arrIMG[k].getAttribute('className')=='off'){
				arrIMG[k].onmouseover = function () {this.src = str_replace('-off','-on',this.src);}
				arrIMG[k].onmouseout = function () {this.src = str_replace('-on','-off',this.src);}}}}
}

function str_replace(a, b, str) {
    return str_replace2(str, a, b);
}

function str_replace2(SRs, SRt, SRu) {
  SRRi = SRs.indexOf(SRt);
  SRRr = '';
  if (SRRi == -1) return SRs;
  SRRr += SRs.substring(0,SRRi) + SRu;
  if ( SRRi + SRt.length < SRs.length) SRRr += str_replace2(SRs.substring(SRRi + SRt.length, SRs.length), SRt, SRu);
  return SRRr;
}

initNavigation();