Fix out of bounds index access in getLabelMoment

Previously, calling getLabelMoment with an out of bound index would cause an
error such as this:

```
Uncaught TypeError: Cannot read property 'null' of undefined
```

This happens because there is not always guaranteed to be a labelMoment on
at the current datasetIndex.

One example of this is practice comes from a this function call:

```js
// since the are not always guaranteed to be at least two labelMoments
//                                \ / this index can be out of bounds
//                                 |
var tickWidth = me.getPixelForTick(1) - me.getPixelForTick(0) - 6;
```

This patch simply ensures that the `labelMoments` for the `datasetIndex` are
defined before accessing properties on it.

diff --git a/src/scales/scale.time.js b/src/scales/scale.time.js
index c409947782362972bf34f38a76de24d0c56436da..91ac3aa0778c57a8211231fe1d3f87dbbf478225 100755 (executable)
--- a/src/scales/scale.time.js
+++ b/src/scales/scale.time.js
@@ -76,7 +76,11 @@ module.exports = function(Chart) {
                        Chart.Scale.prototype.initialize.call(this);
                },
                getLabelMoment: function(datasetIndex, index) {
-                       return this.labelMoments[datasetIndex][index];
+                       if (typeof this.labelMoments[datasetIndex] != 'undefined') {
+                               return this.labelMoments[datasetIndex][index];
+                       }
+
+                       return null;
                },
                getMomentStartOf: function(tick) {
                        var me = this;

diff --git a/test/scale.time.tests.js b/test/scale.time.tests.js
index f3173e1c455e779187540a723350719bf6070534..88a21dda6c25a3772680944d6fdcaf9859031689 100755 (executable)
--- a/test/scale.time.tests.js
+++ b/test/scale.time.tests.js
@@ -479,4 +479,33 @@ describe('Time scale tests', function() {
                        threshold: 0.75
                });
        });
+
+       it("should not throw an error if the datasetIndex is out of bounds", function() {
+               var chart = window.acquireChart({
+                       type: 'line',
+                       data: {
+                               labels: ["2016-06-26"],
+                               datasets: [{
+                                       type: "line",
+                                       data: [5]
+                               }]
+                       },
+                       options: {
+                               scales: {
+                                       xAxes: [{
+                                               display: true,
+                                               type: "time",
+                                       }]
+                               }
+                       }
+               });
+
+               var xScale = chartInstance.scales.xScale0;
+
+               var getOutOfBoundPixelForValue = function() {
+                       xScale.getLabelMoment(12, 0);
+               };
+
+               expect(getOutOfBoundPixelForValue).not.toThrow();
+       });
 });