[added] Add elementToFocus prop

lib/components/Tray.js

@@ -12,7 +12,8 @@ export default React.createClass({
     onOpen: React.PropTypes.func,
     closeTimeoutMS: React.PropTypes.number,
     closeOnBlur: React.PropTypes.bool,
-    maintainFocus: React.PropTypes.bool
+    maintainFocus: React.PropTypes.bool,
+    elementToFocus: React.PropTypes.string
   },
 
   getDefaultProps() {

lib/components/TrayPortal.js

@@ -58,7 +58,8 @@ export default React.createClass({
     closeOnBlur: PropTypes.bool,
     closeTimeoutMS: PropTypes.number,
     children: PropTypes.any,
-    maintainFocus: PropTypes.bool
+    maintainFocus: PropTypes.bool,
+    elementToFocus: PropTypes.string
   },
 
   getInitialState() {
@@ -86,7 +87,11 @@ export default React.createClass({
 
   componentDidUpdate() {
     if (this.focusAfterRender) {
-      this.focusContent();
+      if (this.props.elementToFocus) {
+        this.focusSelector(this.props.elementToFocus);
+      } else {
+        this.focusContent();
+      }
       this.setFocusAfterRender(false);
     }
   },
@@ -99,6 +104,12 @@ export default React.createClass({
     this.refs.content.focus();
   },
 
+  focusSelector(querySelectorToUse) {
+    const el = document.querySelectorAll(querySelectorToUse);
+    const element = (el.length) ? el[0] : el;
+    element.focus();
+  },
+
   handleOverlayClick(e) {
     if (!isChild(this.refs.content, e.target)) {
       this.props.onBlur();

lib/components/__tests__/Tray-test.js

@@ -116,4 +116,23 @@ describe('react-tray', function() {
       equal(document.activeElement, lastItem);
     });
   });
+
+  describe('focusAfterOpen prop', function() {
+    beforeEach(function(done) {
+      const props = {isOpen: true, onBlur: function() {}, closeTimeoutMS: 0, maintainFocus: true, focusAfterOpen: '#two'};
+      const children = (
+        <div>
+          <a href="#" id="one">One</a>
+          <a href="#" id="two">Two</a>
+          <a href="#" id="three">Three</a>
+        </div>
+      );
+      renderTray(props, children, () => done());
+    });
+
+    it('sends focus to the DOM node found via the selector passed in the prop', function() {
+      const secondItem = document.querySelector('#two');
+      equal(document.activeElement, secondItem);
+    });
+  });
 });