add on demand mode loading to cm.

src/dropdown.js

@@ -0,0 +1,30 @@
+// Dropdown.js
+
+(function($all) {
+	var openDropdown;
+
+	// Closes all dropdowns except the passed one.
+	function closeOpenDropdown(except) {
+		if (openDropdown && (!except || except !== openDropdown)) {
+			openDropdown.classList.remove('open');
+			openDropdown = null;
+		}
+	}
+	function init() {
+		var dropdowns = [].slice.call($all('[dropdown]'));
+		dropdowns.forEach(function (dropdown) {
+			dropdown.addEventListener('click', function (e) {
+				closeOpenDropdown(e.currentTarget);
+				e.currentTarget.classList.toggle('open');
+				openDropdown = e.currentTarget;
+				e.stopPropagation();
+			});
+		});
+
+		document.addEventListener('click', function () {
+			closeOpenDropdown();
+		});
+	}
+
+	init();
+})($all);