Version 1.17.0: add toExcel() and toUtcExcel()

README.md

@@ -6,7 +6,7 @@
 ![license](http://img.shields.io/npm/l/timezonecomplete.svg)
 
 [![NPM](https://nodei.co/npm/timezonecomplete.png?downloads=true&downloadRank=true&stars=true)](https://nodei.co/npm/timezonecomplete/)
-[![NPM](https://nodei.co/npm-dl/timezonecomplete.png?months=6&height=3)](https://nodei.co/npm/timezonecomplete/)
+[![NPM](https://nodei.co/npm-dl/timezonecomplete.png?months=9&height=3)](https://nodei.co/npm/timezonecomplete/)
 
 
 ## Synopsis
@@ -359,7 +359,12 @@ var amsterdamDateNoDst = new tc.DateTime(2014, 1, 1, 13, 59, 59, 0, tc.zone("Eur
 var amsterdamDateFromString = new tc.DateTime("2014-01-01T13:59:59.000 Europe/Amsterdam");
 
 // date from an Excel datetime number
-var excelDate = tc.DateTime.fromExcel(42005.5430555556); // 2015-01-01T13:02:00
+var dt = tc.DateTime.fromExcel(42005.5430555556); // 2015-01-01T13:02:00
+
+// Excel datetime number from a data
+var dt = new tc.DateTime("2015-01-01T13:02:00 Europe/Amsterdam");
+var excelAmsterdam = dt.toExcel(); // 42005.5430555556
+var excelUtc = dt.toUtcExcel(); // 42005.501388888933333333333333333 (one hour earlier)
 
 // a fully aware time without Daylight Saving Time: a fixed offset from UTC of 2 hours
 var fixedOffset;
@@ -617,6 +622,8 @@ The version of the included IANA time zone database is 2015b.
 
 ## Changelog
 
+### 1.17.0 (2015-03-30)
+* Add DateTime#toExcel() and DateTime#toUtcExcel() functions to convert a DateTime to a Microsoft Excel date/time number.
 
 ### 1.16.1 (2015-03-26)
 * Make DateTime constructor robust with respect to fractional numbers (it rounds to nearest millisecond)

dist/timezonecomplete.js

@@ -924,11 +924,39 @@ var DateTime = (function () {
     /**
      * Create a DateTime from a Lotus 123 / Microsoft Excel date-time value
      * i.e. a double representing days since 1-1-1900 where 1900 is incorrectly seen as leap year
+     * Does not work for dates < 1900
+     * @param n excel date/time number
+     * @param timeZone Time zone to assume that the excel value is in
+     * @returns a DateTime
      */
     DateTime.fromExcel = function (n, timeZone) {
         var unixTimestamp = Math.round((n - 25569) * 24 * 60 * 60 * 1000);
         return new DateTime(unixTimestamp, timeZone);
     };
+    /**
+     * Create an Excel timestamp for this datetime converted to the given zone.
+     * Does not work for dates < 1900
+     * @param timeZone Optional. Zone to convert to, default the zone the datetime is already in.
+     * @return an Excel date/time number i.e. days since 1-1-1900 where 1900 is incorrectly seen as leap year
+     */
+    DateTime.prototype.toExcel = function (timeZone) {
+        var dt = this;
+        if (timeZone && !timeZone.equals(this.zone())) {
+            dt = this.toZone(timeZone);
+        }
+        var offsetMillis = dt.offset() * 60 * 1000;
+        var unixTimestamp = dt.unixUtcMillis();
+        return ((unixTimestamp + offsetMillis) / (24 * 60 * 60 * 1000)) + 25569;
+    };
+    /**
+     * Create an Excel timestamp for this datetime converted to UTC
+     * Does not work for dates < 1900
+     * @return an Excel date/time number i.e. days since 1-1-1900 where 1900 is incorrectly seen as leap year
+     */
+    DateTime.prototype.toUtcExcel = function () {
+        var unixTimestamp = this.unixUtcMillis();
+        return ((unixTimestamp) / (24 * 60 * 60 * 1000)) + 25569;
+    };
     /**
      * @return a copy of this object
      */