CDE

Task/Date-manipulation/JavaScript/date-manipulation.js

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+function add12hours(dateString) {
+
+  // Get the parts of the date string
+  var parts = dateString.split(/\s+/);
+  var date  = parts[1];
+  var month = parts[0];
+  var year  = parts[2];
+  var time  = parts[3];
+  var ampm  = time && time.match(/[a-z]+$/i)[0];
+  var hr    = Number(time.split(':')[0]);
+  var min   = Number(time.split(':')[1].replace(/\D/g,''));
+  var zone  = parts[4].toUpperCase();
+  var months = ['January','February','March','April','May','June',
+     'July','August','September','October','November','December'];
+  var zones = {'EST': 300, 'AEST': -600}; // Minutes to add to zone time to get UTC
+
+  // Convert month name to number, zero indexed
+  // Could use indexOf but not supported widely
+  for (var i=0, iLen=months.length; i<iLen; i++) {
+    if (months[i] == month) {
+      month = i;
+    }
+  }
+  if (typeof month != 'number') return; // Invalid month name provided
+
+  // Convert hours to 24hr
+  if (ampm && ampm.toLowerCase() == 'pm') {
+    hr += 12;
+  }
+
+  // Add 12 hours to hours
+  hr += 12;
+
+  // Create a date object in local zone
+  var d = new Date(year, month, date);
+  d.setHours(hr, min, 0, 0);
+
+  // Adjust minutes for the time zones
+  d.setMinutes(d.getMinutes() + zones[zone] - d.getTimezoneOffset() );
+
+  // d is now a local date representing the same moment as the
+  // source date plus 12 hours
+  return d;
+}
+
+var inputDateString = 'March 7 2009 7:30pm EST';
+
+alert(
+  'Input: ' + inputDateString + '\n' +
+  '+12hrs in local time: ' + add12hours(inputDateString)
+ );