/* 
	Get Element of a DOM Node by its class name
*/
function getElementsByClassName(node, classname)
{
    var a = [];
    var re = new RegExp('\\b' + classname + '\\b');
    var els = node.getElementsByTagName("*");
    for(var i=0,j=els.length; i<j; i++)
        if(re.test(els[i].className))a.push(els[i]);
    return a;
}

var defaultFontSize = 12;
var currentFontSize = defaultFontSize;

function changeFontSize(sizeDifference){
	if(sizeDifference == 0) {
		currentFontSize = defaultFontSize;
	} else {
		currentFontSize = parseInt(currentFontSize) + parseInt(sizeDifference);
		if(currentFontSize > 15){
			currentFontSize = 15;
		}else if(currentFontSize < 10){
			currentFontSize = 10;
		}
	}

	setFontSize(currentFontSize);
};

function setFontSize(fontSize){
	document.body.style.fontSize = fontSize + 'px';
};