validate scrollContainer prop for server side

Author: jscottsmith

src/components/ParallaxProvider.js

@@ -3,6 +3,7 @@ import PropTypes from 'prop-types';
 import ParallaxContext from '../helpers/ParallaxContext';
 import ParallaxController from '../classes/ParallaxController';
 import { VERTICAL, HORIZONTAL } from '../constants';
+import validHTMLElement from '../utils/validHTMLElement';
 
 const createController = options => {
     // Don't initialize on the server
@@ -23,7 +24,7 @@ export default class ParallaxProvider extends Component {
     static propTypes = {
         children: PropTypes.node.isRequired,
         scrollAxis: PropTypes.oneOf([VERTICAL, HORIZONTAL]),
-        scrollContainer: PropTypes.instanceOf(Element),
+        scrollContainer: validHTMLElement,
     };
 
     constructor(props) {

src/utils/validHTMLElement.js

@@ -0,0 +1,22 @@
+export default function validHTMLElement(
+    props,
+    propName,
+    componentName = 'ANONYMOUS'
+) {
+    if (typeof window === 'undefined') {
+        return null;
+    }
+
+    if (props[propName]) {
+        const value = props[propName];
+        const isValid = value instanceof window.Element;
+
+        if (!isValid) {
+            return new Error(
+                `Prop name "${propName}" in <${componentName}> must be an HTML DOM element.`
+            );
+        }
+    }
+
+    return null;
+}