[added] Prop for adding aria-hidden to application element (#8)

This makes it so that when provided function that returns a DOM
node to the getAriaHideElement prop,  it will augment that element
with the aria-hidden attribute effectively hiding everything except
the tray from screenreaders.

lib/components/Tray.js

@@ -1,6 +1,7 @@
 import React from 'react';
 import ReactDOM from 'react-dom';
 import TrayPortal from './TrayPortal';
+import { a11yFunction } from '../helpers/customPropTypes';
 const renderSubtreeIntoContainer = ReactDOM.unstable_renderSubtreeIntoContainer;
 
 export default React.createClass({
@@ -13,7 +14,8 @@ export default React.createClass({
     closeTimeoutMS: React.PropTypes.number,
     closeOnBlur: React.PropTypes.bool,
     maintainFocus: React.PropTypes.bool,
-    elementToFocus: React.PropTypes.string
+    elementToFocus: React.PropTypes.string,
+    getAriaHideElement: a11yFunction
   },
 
   getDefaultProps() {

lib/components/TrayPortal.js

@@ -59,7 +59,8 @@ export default React.createClass({
     closeTimeoutMS: PropTypes.number,
     children: PropTypes.any,
     maintainFocus: PropTypes.bool,
-    elementToFocus: PropTypes.string
+    elementToFocus: PropTypes.string,
+    getAriaHideElement: PropTypes.func
   },
 
   getInitialState() {
@@ -104,12 +105,25 @@ export default React.createClass({
     this.refs.content.focus();
   },
 
-  focusSelector(querySelectorToUse) {
+  findSingleElement(querySelectorToUse) {
     const el = document.querySelectorAll(querySelectorToUse);
     const element = (el.length) ? el[0] : el;
+    return element;
+  },
+
+  focusSelector(querySelectorToUse) {
+    const element = this.findSingleElement(querySelectorToUse);
     element.focus();
   },
 
+  toggleAriaHidden(element) {
+    if (!element.getAttribute('aria-hidden')) {
+      element.setAttribute('aria-hidden', true);
+    } else {
+      element.removeAttribute('aria-hidden');
+    }
+  },
+
   handleOverlayClick(e) {
     if (!isChild(this.refs.content, e.target)) {
       this.props.onBlur();
@@ -144,6 +158,9 @@ export default React.createClass({
       if (this.props.onOpen) {
         this.props.onOpen();
       }
+      if (this.props.getAriaHideElement) {
+        this.toggleAriaHidden(this.props.getAriaHideElement());
+      }
       this.setState({afterOpen: true});
     });
   },
@@ -154,6 +171,9 @@ export default React.createClass({
     } else {
       this.closeWithoutTimeout();
     }
+    if (this.props.getAriaHideElement) {
+      this.toggleAriaHidden(this.props.getAriaHideElement());
+    }
   },
 
   closeWithTimeout() {

lib/components/__tests__/Tray-test.js

@@ -135,4 +135,31 @@ describe('react-tray', function() {
       equal(document.activeElement, secondItem);
     });
   });
+
+  describe('getAriaHideElement prop', function() {
+    const getAriaHideElement = () => {
+      return document.getElementById('main_application_div');
+    };
+
+    beforeEach(function() {
+      const mainDiv = document.createElement('div');
+      mainDiv.id = 'main_application_div';
+      document.body.appendChild(mainDiv);
+    });
+
+    it('adds aria-hidden to the given element when open', function() {
+      renderTray({isOpen: true, getAriaHideElement: getAriaHideElement});
+      const el = document.getElementById('main_application_div');
+      equal(el.getAttribute('aria-hidden'), 'true');
+    });
+
+    it('removes aria-hidden from the given element when closed', function() {
+      renderTray({isOpen: true, onBlur: function() {}, closeTimeoutMS: 0, getAriaHideElement: getAriaHideElement});
+      TestUtils.Simulate.keyDown(document.querySelector('.ReactTray__Content'), {key: 'Esc'});
+      setTimeout(function() {
+        const el = document.getElementById('main_application_div');
+        equal(el.getAttribute('aria-hidden'), null);
+      }, 0);
+    });
+  });
 });

lib/helpers/customPropTypes.js

@@ -0,0 +1,10 @@
+// Adapted from https://github.com/react-bootstrap/react-prop-types/blob/master/src/isRequiredForA11y.js
+export function a11yFunction(props, propName, componentName) {
+  if ((!props[propName]) || (typeof props[propName] !== 'function')) {
+    return new Error(
+      `The prop '${propName}' is required to make '${componentName}' fully accessible. ` +
+      `This will greatly improve the experience for users of assistive technologies. ` +
+      `You should provide a function that returns a DOM node.`
+    );
+  }
+}