ensure unhover event is not emitted if beforehover handler returns false

Author: emilykl

src/components/dragelement/unhover.js

@@ -16,14 +16,14 @@ unhover.wrapped = function(gd, evt, subplot) {
         throttle.clear(gd._fullLayout._uid + hoverConstants.HOVERID);
     }
 
-    var oldhoverdata = gd._hoverdata;
+    const oldhoverdata = gd._hoverdata;
 
-    unhover.raw(gd, evt, subplot);
+    const shouldEmitUnhover = unhover.raw(gd, evt, subplot);
 
     // Special handling for `hoveranywhere`, to ensure we emit exactly one unhover event
     // when the cursor leaves the plot area.
     // gd._hoverAnywhereActive is set in fx/hover.js when we emit an empty-space hover event.
-    if(gd._hoverAnywhereActive) {
+    if(shouldEmitUnhover && gd._hoverAnywhereActive) {
         gd._hoverAnywhereActive = false;
 
         // Make sure hoveranywhere is still enabled
@@ -38,14 +38,16 @@ unhover.wrapped = function(gd, evt, subplot) {
 
 
 // remove hover effects on mouse out, and emit unhover event
+// returns false if unhover was skipped due to the plotly_beforehover handler returning false;
+// returns true otherwise
 unhover.raw = function raw(gd, evt) {
     var fullLayout = gd._fullLayout;
     var oldhoverdata = gd._hoverdata;
 
     if(!evt) evt = {};
     if(evt.target && !gd._dragged &&
        Events.triggerHandler(gd, 'plotly_beforehover', evt) === false) {
-        return;
+        return false;
     }
 
     fullLayout._hoverlayer.selectAll('g').remove();
@@ -59,4 +61,5 @@ unhover.raw = function raw(gd, evt) {
             points: oldhoverdata
         });
     }
+    return true;
 };