New function: calculate index of start timestamp

public/js/src_modules/aggregateHelpers.mjs

@@ -60,19 +60,36 @@ const checkIfLeapYear = function (year) {
  * @returns {Number} An integer representing the index of the timestamp of interest in the array of timestamps
  */
 const getIndexOfTimestamp = function (inputTimestampArr, timestampOfInterest) {
-  const timestampIndex = inputTimestampArr.findIndex(
+  return inputTimestampArr.findIndex(
     (timestamp) => timestamp === timestampOfInterest
   );
+};
+
+/**
+ * Calculate the index of a start timestamp in an array of timestamps
+ *
+ * @param {Array} inputTimestampArr An array of timestamps, extracted from an array of observations
+ * @param {String} timestampOfInterest A string representing the timestamp of interest in ISO 8601 format
+ * @returns {Number} An integer representing the index of the timestamp of interest in the array of timestamps
+ */
+const getIndexOfStartTimestamp = function (
+  inputTimestampArr,
+  timestampOfInterest
+) {
+  const timestampStartIndex = getIndexOfTimestamp(
+    inputTimestampArr,
+    timestampOfInterest
+  );
 
   // If the timestamp does not exist in the timestamp array
-  if (timestampIndex === -1) {
+  if (timestampStartIndex === -1) {
     throw new Error(
-      "A start or end timestamp could not be found in the timestamp array"
+      "A start timestamp could not be found in the timestamp array"
     );
   }
   // If the timestamp exists in the timestamp array
   else {
-    return timestampIndex;
+    return timestampStartIndex;
   }
 };