From e4dd158b241268600bb1c9005969af7b2efcb130 Mon Sep 17 00:00:00 2001
From: Ian Ker-Seymer <i.kerseymer@gmail.com>
Date: Tue, 26 Jul 2016 14:45:05 -0400
Subject: [PATCH] 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.
---
 src/scales/scale.time.js |  6 +++++-
 test/scale.time.tests.js | 29 +++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/src/scales/scale.time.js b/src/scales/scale.time.js
index c4099477823..91ac3aa0778 100755
--- 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 f3173e1c455..88a21dda6c2 100755
--- 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();
+	});
 });