Merge branch 'ponty96-fix/document-ssr'

# Please enter a commit message to explain why this merge is necessary,
# especially if it merges an updated upstream into a topic branch.
#
# Lines starting with '#' will be ignored, and an empty message aborts
# the commit.

Author: Malte W

src/Scrollbars.js

@@ -303,23 +303,25 @@ export default createClass({
     },
 
     addListeners() {
+        if (typeof document === 'undefined') return;
         this.refs.view.addEventListener('scroll', this.handleScroll);
         this.refs.barVertical.addEventListener('mousedown', this.handleVerticalTrackMouseDown);
         this.refs.barHorizontal.addEventListener('mousedown', this.handleHorizontalTrackMouseDown);
         this.refs.thumbVertical.addEventListener('mousedown', this.handleVerticalThumbMouseDown);
         this.refs.thumbHorizontal.addEventListener('mousedown', this.handleHorizontalThumbMouseDown);
-        if (document) document.addEventListener('mouseup', this.handleDocumentMouseUp);
-        if (window) window.addEventListener('resize', this.handleWindowResize);
+        document.addEventListener('mouseup', this.handleDocumentMouseUp);
+        window.addEventListener('resize', this.handleWindowResize);
     },
 
     removeListeners() {
+        if (typeof document === 'undefined') return;
         this.refs.view.removeEventListener('scroll', this.handleScroll);
         this.refs.barVertical.removeEventListener('mousedown', this.handleVerticalTrackMouseDown);
         this.refs.barHorizontal.removeEventListener('mousedown', this.handleHorizontalTrackMouseDown);
         this.refs.thumbVertical.removeEventListener('mousedown', this.handleVerticalThumbMouseDown);
         this.refs.thumbHorizontal.removeEventListener('mousedown', this.handleHorizontalThumbMouseDown);
-        if (document) document.removeEventListener('mouseup', this.handleDocumentMouseUp);
-        if (window) window.removeEventListener('resize', this.handleWindowResize);
+        document.removeEventListener('mouseup', this.handleDocumentMouseUp);
+        window.removeEventListener('resize', this.handleWindowResize);
     },
 
     render() {

src/utils/getScrollbarWidth.js

@@ -3,7 +3,7 @@ let scrollbarWidth = false;
 
 export default function getScrollbarWidth() {
     if (scrollbarWidth !== false) return scrollbarWidth;
-    if (document) {
+    if (typeof document !== 'undefined') {
         const div = document.createElement('div');
         css(div, {
             width: 100,