<select id="location">
<option value="loc1">Location 1</option>
<option value="loc2">Location 2</option>
<option value="loc3">Location 3</option>
<option value="loc4">Location 4</option>
<option value="loc5">Location 5</option>
<option value="loc6">Location 6</option>
<option value="loc7">Location 7</option>
</select>
<select id="second">
<option value="OPT1">Option 1</option>
<option value="OPT2">Option 2</option>
<option value="OPT3">Option 3</option>
<option value="OPT4">Option 4</option>
</select>
var source = document.getElementById("location");
var target = document.getElementById("second");
var triggerValue = "loc5";
function toggleShowOnSelectedValue(evt) {
var selectedValue = this[this.selectedIndex].value;
if (selectedValue === triggerValue) {
target.className = "show";
} else {
target.className = "";
}
};
//source.onchange = toggleShowOnSelectedValue;
source.addEventListener("change", toggleShowOnSelectedValue, false);