Correct Answer:
function addDays(date, days) { var result = new Date(date); result.setDate(result.getDate() + days); return result;}
Incorrect Answer:
This answer sometimes provides the correct result but very often returns the wrong year and month. The only time this answer works is when the date that you are adding days to happens to have the current year and month.
function addDaysWRONG(date, days) { var result = new Date(); result.setDate(date.getDate() + days); return result;}
Proof / Example
Check this JsFiddle
function addDays(date, days) { var result = new Date(date); result.setDate(result.getDate() + days); return result;}function addDaysWRONG(date, days) { var result = new Date(); result.setDate(date.getDate() + days); return result;}function addDaysDstFail(date, days) { var dayms = (days * 24 * 60 * 60 * 1000); return new Date(date.getTime() + dayms); }function formatDate(date) { return (date.getMonth() + 1) + '/' + date.getDate() + '/' + date.getFullYear();}$('tbody tr td:first-child').each(function () { var $in = $(this); var $out = $('<td/>').insertAfter($in).addClass("answer"); var $outFail = $('<td/>').insertAfter($out); var $outDstFail = $('<td/>').insertAfter($outFail); var date = new Date($in.text()); var correctDate = formatDate(addDays(date, 1)); var failDate = formatDate(addDaysWRONG(date, 1)); var failDstDate = formatDate(addDaysDstFail(date, 1)); $out.text(correctDate); $outFail.text(failDate); $outDstFail.text(failDstDate); $outFail.addClass(correctDate == failDate ? "right" : "wrong"); $outDstFail.addClass(correctDate == failDstDate ? "right" : "wrong");});
body { font-size: 14px;}table { border-collapse:collapse;}table, td, th { border:1px solid black;}td { padding: 2px;}.wrong { color: red;}.right { color: green;}.answer { font-weight: bold;}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script><table> <tbody> <tr> <th colspan="4">DST Dates</th> </tr> <tr> <th>Input</th> <th>+1 Day</th> <th>+1 Day Fail</th> <th>+1 Day DST Fail</th> </tr> <tr><td>03/10/2013</td></tr> <tr><td>11/03/2013</td></tr> <tr><td>03/09/2014</td></tr> <tr><td>11/02/2014</td></tr> <tr><td>03/08/2015</td></tr> <tr><td>11/01/2015</td></tr> <tr> <th colspan="4">2013</th> </tr> <tr> <th>Input</th> <th>+1 Day</th> <th>+1 Day Fail</th> <th>+1 Day DST Fail</th> </tr> <tr><td>01/01/2013</td></tr> <tr><td>02/01/2013</td></tr> <tr><td>03/01/2013</td></tr> <tr><td>04/01/2013</td></tr> <tr><td>05/01/2013</td></tr> <tr><td>06/01/2013</td></tr> <tr><td>07/01/2013</td></tr> <tr><td>08/01/2013</td></tr> <tr><td>09/01/2013</td></tr> <tr><td>10/01/2013</td></tr> <tr><td>11/01/2013</td></tr> <tr><td>12/01/2013</td></tr> <tr> <th colspan="4">2014</th> </tr> <tr> <th>Input</th> <th>+1 Day</th> <th>+1 Day Fail</th> <th>+1 Day DST Fail</th> </tr> <tr><td>01/01/2014</td></tr> <tr><td>02/01/2014</td></tr> <tr><td>03/01/2014</td></tr> <tr><td>04/01/2014</td></tr> <tr><td>05/01/2014</td></tr> <tr><td>06/01/2014</td></tr> <tr><td>07/01/2014</td></tr> <tr><td>08/01/2014</td></tr> <tr><td>09/01/2014</td></tr> <tr><td>10/01/2014</td></tr> <tr><td>11/01/2014</td></tr> <tr><td>12/01/2014</td></tr> <tr> <th colspan="4">2015</th> </tr> <tr> <th>Input</th> <th>+1 Day</th> <th>+1 Day Fail</th> <th>+1 Day DST Fail</th> </tr> <tr><td>01/01/2015</td></tr> <tr><td>02/01/2015</td></tr> <tr><td>03/01/2015</td></tr> <tr><td>04/01/2015</td></tr> <tr><td>05/01/2015</td></tr> <tr><td>06/01/2015</td></tr> <tr><td>07/01/2015</td></tr> <tr><td>08/01/2015</td></tr> <tr><td>09/01/2015</td></tr> <tr><td>10/01/2015</td></tr> <tr><td>11/01/2015</td></tr> <tr><td>12/01/2015</td></tr> </tbody></table>