don't clear gd.data when both fullReplot & layoutReplot are true

... during Plotly.update. Clearing gd.data lead to an erroneous
    makePlotFramework call which lead to modebar buttons not displaying
    (and potentially other bugs)

Author: etpinard

src/plot_api/plot_api.js

@@ -2362,20 +2362,12 @@ function update(gd, traceUpdate, layoutUpdate, _traces) {
     // fill in redraw sequence
     var seq = [];
 
-    if(restyleFlags.fullReplot && relayoutFlags.layoutReplot) {
-        var data = gd.data;
-        var layout = gd.layout;
-
-        // clear existing data/layout on gd
-        // so that Plotly.plot doesn't try to extend them
-        gd.data = undefined;
-        gd.layout = undefined;
-
-        seq.push(function() { return exports.plot(gd, data, layout); });
+    if(relayoutFlags.layoutReplot) {
+        // N.B. works fine when both
+        // relayoutFlags.layoutReplot and restyleFlags.fullReplot are true
+        seq.push(subroutines.layoutReplot);
     } else if(restyleFlags.fullReplot) {
         seq.push(exports.plot);
-    } else if(relayoutFlags.layoutReplot) {
-        seq.push(subroutines.layoutReplot);
     } else {
         seq.push(Plots.previousPromises);
         axRangeSupplyDefaultsByPass(gd, relayoutFlags, relayoutSpecs) || Plots.supplyDefaults(gd);

test/jasmine/tests/plot_api_test.js

@@ -2650,16 +2650,29 @@ describe('Test plot api', function() {
         it('should only have one modebar-container', function(done) {
             var data = [{y: [1, 2]}];
 
-            Plotly.plot(gd, data).then(function() {
-                var modebars = document.getElementsByClassName('modebar-container');
-                expect(modebars.length).toBe(1);
+            function _assert(msg) {
+                return function() {
+                    var modebars = document.getElementsByClassName('modebar-container');
+                    expect(modebars.length).toBe(1, msg + ' # of modebar container');
+                    var groups = document.getElementsByClassName('modebar-group');
+                    expect(groups.length).toBe(5, msg + ' # of modebar button groups');
+                };
+            }
 
-                return Plotly.newPlot(gd, data);
-            })
-            .then(function() {
-                var modebars = document.getElementsByClassName('modebar-container');
-                expect(modebars.length).toBe(1);
+            Plotly.plot(gd, data)
+            .then(_assert('base'))
+            .then(function() { return Plotly.newPlot(gd, data); })
+            .then(_assert('after newPlot()'))
+            .then(function() {
+                // funky combinations of update flags found in
+                // https://github.com/plotly/plotly.js/issues/3824
+                return Plotly.update(gd, {
+                    visible: false
+                }, {
+                    annotations: [{text: 'a'}]
+                });
             })
+            .then(_assert('after update()'))
             .catch(failTest)
             .then(done);
         });