classToggleHelper.js

// usage:
openToggler(getElement('#some-element'), getElement('#some-element-dropdown'));

// code:
function openToggler(clicker, target) {
	if (!clicker || !target) return;
	var setter = classSetter(target, 'open');
	var opened = false;
	var clickHandler = function (e) {
		opened = !opened;
		setter(opened);
		if (opened) {
			setTimeout(function () {
				document.body.addEventListener('click', clickHandler, false);
			});
		} else {
			document.body.removeEventListener('click', clickHandler, false);
		}
	};
	clicker.addEventListener('click', clickHandler, false);
}

function classSetter(anchor, className) {
	return function (on) {
		var oldClassNames = anchor.className.split(/\s+/);
		var idx = oldClassNames.indexOf(className);
		var hasClass = !!~idx;
		if (on) {
			if (!hasClass) {
				oldClassNames.push(className)
				anchor.className = oldClassNames.join(' ');
			}
		} else {
			if (hasClass) {
				oldClassNames.splice(idx, 1);
				anchor.className = oldClassNames.join(' ');
			}
		}
	}
}

function getElement(selector) {
	return document.querySelector(selector);
}