fix(commons/dom): focusDisabled() behavior

Now checks "disabled" attribute

Closes issue #3315

lib/commons/dom/focus-disabled.js

@@ -2,6 +2,13 @@ import AbstractVirtualNode from '../../core/base/virtual-node/abstract-virtual-n
 import { getNodeFromTree } from '../../core/utils';
 import isHiddenWithCSS from './is-hidden-with-css';
 
+function isDisabledAttrAllowed(nodeName) {
+  // Source: https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/disabled 
+  const allowedNodeNames = new Set(["button", "command", "fieldset", "keygen", "optgroup", 
+      "option", "select", "textarea", "input"]);
+  return allowedNodeNames.has(nodeName);
+}
+
 /**
  * Determines if focusing has been disabled on an element.
  * @param {HTMLElement|VirtualNode} el The HTMLElement
@@ -10,7 +17,7 @@ import isHiddenWithCSS from './is-hidden-with-css';
 function focusDisabled(el) {
   const vNode = el instanceof AbstractVirtualNode ? el : getNodeFromTree(el);
 
-  if (vNode.hasAttr('disabled')) {
+  if (isDisabledAttrAllowed(vNode.props.nodeName) && vNode.hasAttr('disabled')) {
     return true;
   }
 

test/checks/keyboard/no-focusable-content.js

@@ -93,6 +93,13 @@ describe('no-focusable-content tests', function() {
     assert.isTrue(noFocusableContent(null, null, vNode));
   });
 
+  it('should return false if "disabled" is specified on an element which doesn\'t allow it', function() {
+    var params = checkSetup(
+      '<button id="target"><a href="foo.html" disabled>Hello</a></button>'
+    );
+    assert.isFalse(noFocusableContent.apply(checkContext, params));
+  });
+
   it('should return true on span with negative tabindex (focusable, does not have a widget role)', function() {
     var vNode = queryFixture('<span id="target" role="text"> some text '
         +'<span tabIndex="-1">JavaScript is able to focus this</span> '