I want some JavaScript which can trigger/open select option while someone click on button using below code for select option

```
<div class="period" title="Choose a number of nights">
<span class="label">Nights</span>
<span class="input">
<select rel="period" value="4">
<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>
</select></span></div>

```

Using below code for button

```
<td class="total">
<a class="im-pricebutton has-hover" href="javascript://;" value="A 2 night booking condition applies to this period">
<span class="book im-pricebutton-label">Min 2 nights</span>
<span class="number im-pricebutton-amount">$0</span>
</a></td>

```

As of now I have setup condition of Minimum night select as a 3,5 and 10 it's very on products so when someone don't pass this night function it'll show above code to select minimum night but how to pass some custom JavaScript which can open up drop down automatically when they click on button.