function addLoadEvent(func) {
	var oldonload = window.onload;
	if (typeof window.onload != 'function') {
		window.onload = func;
	} else {
		window.onload = function() {
			oldonload();
			func();
		}
	}
}
function previous() {
	history.go(-1);
	return false;
}
function backOff() {
	if (!document.getElementById) return false;
	if (!document.getElementById("back-to-home")) return false;
	var back_to_home = document.getElementById("back-to-home");
	var back_off = document.createElement("a");
	var text = document.createTextNode("后退");
	back_off.appendChild(text);
	back_off.setAttribute("href","#");
	back_to_home.parentNode.insertBefore(back_off,back_to_home);
	back_off.onclick = previous;
}
addLoadEvent(backOff);