[Plot] Avoid displaying bad labels

Avoid displaying bad labels for tick marks, or in the
coordinates shown on hover. Done in the context of
refactoring to support WTD-625.

platform/features/plot/res/templates/plot.html

@@ -16,8 +16,8 @@
             </div>
 
             <div class="gl-plot-coords"
-                 ng-if="subplot.isHovering()">
+                 ng-if="subplot.isHovering() && subplot.getHoverCoordinates()">
-                {{subplot.getHoverCoordinates().join(', ')}}
+                {{subplot.getHoverCoordinates()}}
             </div>
 
             <div class="gl-plot-axis-area gl-plot-y">

platform/features/plot/src/SubPlot.js

@@ -33,6 +33,7 @@ define(
                 domainOffset,
                 mousePosition,
                 marqueeStart,
+                hoverCoordinates,
                 isHovering = false;
 
             // Utility, for map/forEach loops. Index 0 is domain,
@@ -43,6 +44,11 @@ define(
                         formatter.formatDomainValue)(v);
             }
 
+            // Utility function for filtering out empty strings.
+            function isNonEmpty(v) {
+                return typeof v === 'string' && v !== "";
+            }
+
             // Converts from pixel coordinates to domain-range,
             // to interpret mouse gestures.
             function mousePositionToDomainRange(mousePosition) {
@@ -79,6 +85,16 @@ define(
                 return [ position[0] - domainOffset, position[1] ];
             }
 
+
+            // Update the currnet hover coordinates
+            function updateHoverCoordinates() {
+                hoverCoordinates = mousePosition &&
+                        mousePositionToDomainRange(mousePosition)
+                            .map(formatValue)
+                            .filter(isNonEmpty)
+                            .join(", ");
+            }
+
             // Update the drawable marquee area to reflect current
             // mouse position (or don't show it at all, if no marquee
             // zoom is in progress)
@@ -191,10 +207,7 @@ define(
                  *          coordinates over which the mouse is hovered
                  */
                 getHoverCoordinates: function () {
-                    return mousePosition ?
+                    return hoverCoordinates;
-                            mousePositionToDomainRange(
-                                mousePosition
-                            ).map(formatValue) : [];
                 },
                 /**
                  * Handle mouse movement over the chart area.
@@ -203,6 +216,7 @@ define(
                 hover: function ($event) {
                     isHovering = true;
                     mousePosition = toMousePosition($event);
+                    updateHoverCoordinates();
                     if (marqueeStart) {
                         updateMarqueeBox();
                     }

platform/features/plot/src/elements/PlotFormatter.js

@@ -16,11 +16,11 @@ define(
          */
         function PlotFormatter() {
             function formatDomainValue(v) {
-                return moment.utc(v).format(DATE_FORMAT);
+                return isNaN(v) ? "" : moment.utc(v).format(DATE_FORMAT);
             }
 
             function formatRangeValue(v) {
-                return v.toFixed(1);
+                return isNaN(v) ? "" : v.toFixed(1);
             }
 
             return {

platform/features/plot/test/SubPlotSpec.js

@@ -84,13 +84,15 @@ define(
 
             it("provides hovering coordinates", function () {
                 // Should be empty when not hovering
-                expect(subplot.getHoverCoordinates()).toEqual([]);
+                expect(subplot.getHoverCoordinates())
+                    .toBeUndefined();
 
                 // Start hovering
                 subplot.hover({ target: mockElement });
 
                 // Should now have coordinates to display
-                expect(subplot.getHoverCoordinates().length).toEqual(2);
+                expect(subplot.getHoverCoordinates())
+                    .toEqual(jasmine.any(String));
             });
 
             it("supports marquee zoom", function () {