implement focus events so menu can be tabbed through

README.md

@@ -8,6 +8,7 @@ It handles:
 * Pointer Events
 * Mouse Events
 * Hover Intent
+* Focus Events
 
 If a menu has a top level link and is opened with touch, the menu is opened and the link is not followed.  Then if it is touched again while the menu is open, the link followed.  This behavior is similar to aria-haspopup.
 
@@ -46,3 +47,6 @@ jQuery('#node').dropdown(options);
 * Android 4+ (haven't tested with 2.3)
 * Edge
 * IE8+
+
+### Develop Notes
+Use uglifyjs to create minified version: uglifyjs dropdown.js -o dropdown.min.js --mangle --compress

dropdown.js

@@ -124,7 +124,7 @@ window.Dropdown = (function() {
 			}
 		};
 
-		evts.mouseenter = function(e) {
+		evts.mouseenter = function() {
 			if (typeof _this.timeout.leave === 'number') {
 				window.clearTimeout(_this.timeout.leave);
 			} else {
@@ -134,7 +134,7 @@ window.Dropdown = (function() {
 			}
 		};
 
-		evts.mouseleave = function(e) {
+		evts.mouseleave = function() {
 			if (typeof _this.timeout.enter === 'number') {
 				window.clearTimeout(_this.timeout.enter);
 			} else {
@@ -198,6 +198,35 @@ window.Dropdown = (function() {
 			document.removeEventListener('click', evts.maybeClose);
 		};
 
+		evts.focus = function() {
+			if (!_this.active) {
+				_this.open();
+			}
+		};
+
+		evts.blur = function() {
+			if (_this.menuLinks.length < 1) {
+				_this.close();
+				return;
+			}
+
+			// make this async so we can detect the correct document.activeElement
+			window.setTimeout(function() {
+				for(var i = 0; i<_this.menuLinks.length; i++) {
+					if (document.activeElement === _this.menuLinks[i]) {
+						return;
+					}
+				}
+				_this.close();
+			}, 0);
+		};
+
+		// use event capturing to detect event focus and blur because do not bubble
+		if (this.container.addEventListener) {
+			this.container.addEventListener('focus', evts.focus, true);
+			this.container.addEventListener('blur', evts.blur, true);
+		}
+
 		if (window.PointerEvent) {
 			this.container.addEventListener('pointerenter', evts.pointerenter);
 			this.container.addEventListener('pointerleave', evts.pointerleave);