Merge pull request #4 from HakaiInstitute/bugfix/daylight-savings

Bugfix/daylight savings

Author: jrohland

source/lib/utils.js

@@ -140,14 +140,14 @@ let getExcelRowCol = (str) => {
 let getExcelTS = (date) => {
 
     let thisDt = new Date(date);
-    thisDt.setDate(thisDt.getDate() + 1);
+    thisDt = new Date(thisDt.getTime() + 24 * 60 * 60 * 1000);
 
     let epoch = new Date('1900-01-01T00:00:00.0000Z');
 
     // Handle legacy leap year offset as described in  §18.17.4.1
     const legacyLeapDate = new Date('1900-02-28T23:59:59.999Z');
     if (thisDt - legacyLeapDate > 0) {
-        thisDt.setDate(thisDt.getDate() + 1);
+        thisDt = new Date(thisDt.getTime() + 24 * 60 * 60 * 1000);
     } 
 
     // Get milliseconds between date sent to function and epoch 

tests/library.test.js

@@ -31,6 +31,12 @@ test('Test library functions', (t) => {
     t.equals(xl.getExcelTS(new Date('1900-01-01T12:00:00Z')), 1.5000000, 'Correctly translated date 1900-01-01T12:00:00Z');
     t.equals(xl.getExcelTS(new Date('9999-12-31T23:59:59Z')), 2958465.9999884, 'Correctly translated date 9999-12-31T23:59:59Z');
 
+    /**
+     * getExcelTS should handle dates within 2 days of daylight savings change (2020-03-08 for example)
+     */
+    t.equals(xl.getExcelTS(new Date('2020-03-05T15:38:00Z')), 43895.6513889, 'Correctly translated date 2020-03-01T15:38:00Z');
+    t.equals(xl.getExcelTS(new Date('2020-03-06T15:38:00Z')), 43896.6513889, 'Correctly translated date 2020-03-06T15:38:00Z'); 
+
     /**
      * Tests as defined in §18.17.4.1 of ECMA-376, Second Edition, Part 1 - Fundamentals And Markup Language Reference
      * The serial value 2.0000000... represents 1900-01-01