How does the javaScript function determine how many days there are in this month based on the selected year and month? _html/css

How does the javaScript function determine how many days there are in this month based on the selected year and month? _html/css_WEB-ITnose

WBOY

Release： 2016-06-24 12:20:56

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JavaScript HTML

A drop-down list written in html. I want to determine the number of days in this month based on the selected year and month. How to write a javascript function?

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<script type="text/javascript">function getdate(){var i=document.getElementById('year').value;var j=document.getElementById('month').value;var k=document.getElementById('day').value;return i+"年"+j+"月"+k+"日";}function checkdate(){var select = document.getElementById('day');var year = document.getElementById('year').value;switch(document.getElementById('month').value){case '1':case '3':case '5':case '7':case '8':case '10':case '12':select.length=31;select.options[28].text=29;select.options[29].text=30;select.options[30].text=31;break;case '4':case '6':case '9':case '11':select.length=30;select.options[28].text=29;select.options[29].text=30;break;case '2':if((year%4==0 && year%100!=0) || year%400==0){select.length=29;select.options[28].text=29;}else{select.length=28;}break;default:alert("非法的月份"+document.getElementById('month').value);}}</script><html><body><select name=""id="year" style="width:60px; margin-right:5px" onclick="checkdate();"><option value="1980">1980</option><option value="1981">1981</option><option value="1982">1982</option><option value="1983">1983</option><option value="1984">1984</option><option value="1985">1985</option><option value="1986">1986</option><option value="1987">1987</option><option value="1988">1988</option><option value="1989">1989</option><option value="1990">1990</option><option value="1991">1991</option><option value="1992">1992</option><option value="1993">1993</option><option value="1994">1994</option><option value="1995">1995</option><option value="1996">1996</option><option value="1997">1997</option><option value="1998">1998</option><option value="1999">1999</option><option value="2000">2000</option><option value="2001">2001</option><option value="2002">2002</option><option value="2003">2003</option><option value="2004">2004</option><option value="2005">2005</option><option value="2006">2006</option><option value="2007">2007</option><option value="2008">2008</option><option value="2009">2009</option><option value="2010">2010</option> </select>年<select name="" id="month" style="width:40px;margin-left:5px;" onclick="checkdate();"><option value="1">1</option><option value="2">2</option><option value="3">3</option><option value="4">4</option><option value="5">5</option><option value="6">6</option><option value="7">7</option><option value="8">8</option><option value="9">9</option><option value="10">10</option><option value="11">11</option><option value="12">12</option></select>月<select name=""id="day" style="width:40px; margin-left:5px;" ><option value="1" >1</option><option value="2">2</option><option value="3">3</option><option value="4">4</option><option value="5">5</option><option value="6">6</option><option value="7">7</option><option value="8">8</option><option value="9">9</option><option value="10">10</option><option value="11">11</option><option value="12">12</option><option value="13">13</option><option value="14">14</option><option value="15">15</option><option value="16">16</option><option value="17">17</option><option value="18">18</option><option value="19">19</option><option value="20">20</option><option value="21">21</option><option value="22">22</option><option value="23">23</option><option value="24">24</option><option value="25">25</option><option value="26">26</option><option value="27">27</option><option value="28">28</option><option value="29">29</option><option value="30">30</option><option value="31">31</option></select>日</body></html>

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