[warren buffet]

Вот так делай

function div(){
	var con=mk_div('con');
	con.addEventListener('mousedown', mDown);
	con.addEventListener('mouseup', mUp);
	document.addEventListener('mousemove', mMove);
}

function mk_div(rule){
	var div = document.createElement('div'),
	style=div.style;
	style.width='100px';
	style.height='100px';
	style.backgroundColor="green";
	div.className=rule;
	return document.body.insertBefore(div, document.body.firstChild)
}

btn.onclick = div;