+ // http://jsdo.it/imaya/kTYg
+ body = document.body,
+ defaultOverflow = document.body.style.overflow,
+ w, h;
+
+ body.style.overflow = 'hidden';
+ w = body.clientWidth;
+ h = body.clientHeight;
+
+ body.style.overflow = 'scroll';
+ w -= body.clientWidth;
+ h -= body.clientHeight;
+
+ if( !w ) w = body.offsetWidth - body.clientWidth;
+ if( !h ) h = body.offsetHeight - body.clientHeight;
+ body.style.overflow = defaultOverflow;
+
+ X_ViewPort_vScrollbarSize = w;
+ X_ViewPort_hScrollbarSize = h;
+ if( h <= 0 ){ // ie6, ie11, firefox で 負の値が返る
+ console.log( 'invalid hScrollbarSize: ' + h );
+ X_ViewPort_hScrollbarSize = w;
+ };
+
+ //