Javascript 在原始日期上添加 30 或 20、22 天?

Question

我正在尝试编写一个JavaScript，在您输入的日期中添加10,14,15,20,21,28,30,31,45,49,60,70或90天。唯一的问题是我错过了一些东西。如果有人能提供帮助，那就太好了，或者如果他们的是一个WordPress插件，那就太好了。

我似乎找不到代码中缺少的内容来使其工作

<td id="main_content" valign="top" align="left">
    <div id="date-cal" align="left">
        <br/>
        <div align="left" id="form-field"><strong>Step 1:</strong>
            <br/>Enter your commencement date:
            <br/>
            <span class="tips">
                (eg date of receipt of FOI Request)
            </span>
        </div>
        <form method="post" name="calcform" style="margin-bottom: 0;">
            <span style="font-family: Arial, Helvetica, sans-serif">
                <!-- calendar attaches to existing form element -->
            </span>
            <input type="text" name="txtdate" class="datepicker" value="dd/mm/yy" />
           <script language="JavaScript">
               new tcal ({
                   // form name
                   'formname': 'calcform',
                   // input name
                   'controlname': 'txtdate'
               });
           </script>
            <br />
            <br />
            <div id="form-field2"><strong>Step 2:</strong>
                <br/>Select your relevant period:
                <br/>
                <span class="tips">
                    (eg days to make an FOI decision)
                </span>
            </div>
            <!-- No of days selection dropdown -->
            <select name="daycount">
                <option>10</option>
                <option>14</option>
                <option>15</option>
                <option>20</option>
                <option>21</option>
                <option>28</option>
                <option>30</option>
                <option>31</option>
                <option>45</option>
                <option>49</option>
                <option>60</option>
                <option>70</option>
                <option>90</option>
            </select>
            <label>days</label>
            <p style="margin-top: 0; margin-bottom: 0">
                <br />
                <!-- submit button -->
                <input type="submit" value="Calculate" />
                <br />
            </p>
            <p style="margin-top: 0; margin-bottom: 0;">
                <br />
                <span></span>
            </p>
        </form>
    </div>
</td>

Answer 1

var log = console.log;
var d = new Date();
var daysToAdd = 5; //for example
var msInDay = 1000 * 60 * 60 * 24; //milliseconds in day
log("Before:",d.toLocaleString());
//add 5 days
d.setTime(d.getTime() + daysToAdd * msInDay);
//
log("After :",d.toLocaleString());

Answer 2

替代计算：

<script>
console.clear();
var log = console.log;
var d = new Date();
var daysToAdd = 5; //for example
var msInDay = 1000 * 60 * 60 * 24; //milliseconds in day
log("Before:",d.toLocaleString());
//add 5 days
d.setTime(d.getTime() + daysToAdd * msInDay);
//
log("After :",d.toLocaleString());
// alternative
log()
var d = new Date();
log("Before:",d.toLocaleString());
// add 5 days
d = new Date(d.getFullYear(),d.getMonth(),d.getDate()+5);
//
log("After :",d.toLocaleString());
// Note: can add hours, minutes, seconds if needed.
</script>