silverstripe-betternavigator/javascript/betternavigator.js

//For reading cookies
function getCookie(cname) {
    var name = cname + "=";
    var ca = document.cookie.split(';');
    for(var i=0; i<ca.length; i++) {
        var c = ca[i];
        while (c.charAt(0)===' ') {
        	c = c.substring(1);
        }
        if (c.indexOf(name) !== -1) {
        	return c.substring(name.length,c.length);
        }
    }
    return "";
}

//Do some stuff when the dom is loaded. (Won't work in IE8 or lower)
document.addEventListener("DOMContentLoaded", function() {

	//Dom elements
	var BetterNavigator = document.getElementById("BetterNavigator");
	var BetterNavigatorStatus = document.getElementById("BetterNavigatorStatus");

	//Toggle visibility of menu by clicking status
	BetterNavigatorStatus.onclick=function(){
		BetterNavigator.className = BetterNavigator.className === 'collapsed' ? 'open' : 'collapsed';
		//Set cookie to remember state
		document.cookie="BetterNavigator=" + BetterNavigator.className + ";path=/";
	};
	
	//Restore menu state
	if (getCookie('BetterNavigator') === 'open') {
		BetterNavigator.className = 'open';
	}
	
});