1 files changed, 17 insertions, 0 deletions
diff --git a/app/assets/javascripts/lib/utils/chart_utils.js b/app/assets/javascripts/lib/utils/chart_utils.js
index 0f78756aac8..4a1e6c5d68c 100644
--- a/app/assets/javascripts/lib/utils/chart_utils.js
+++ b/app/assets/javascripts/lib/utils/chart_utils.js
@@ -81,3 +81,20 @@ export const lineChartOptions = ({ width, numberOfPoints, shouldAdjustFontSize }
     },
   },
 });
+
+/**
+ * Takes a dataset and returns an array containing the y-values of it's first and last entry.
+ * (e.g., [['xValue1', 'yValue1'], ['xValue2', 'yValue2'], ['xValue3', 'yValue3']] will yield ['yValue1', 'yValue3'])
+ *
+ * @param {Array} data
+ * @returns {[*, *]}
+ */
+export const firstAndLastY = data => {
+  const [firstEntry] = data;
+  const [lastEntry] = data.slice(-1);
+
+  const firstY = firstEntry[1];
+  const lastY = lastEntry[1];
+
+  return [firstY, lastY];
+};