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How i can show a select list only after another select (parent) has been selected

Like i said in the title i want to keep a list hidden until another another list above has been selected, for example show student list after a class had been selected (so only student who belong to the selected class are shown)
<select name="class">
<option value="">class1</option>
<option value="">class2</option>
</select>
<select name="student">
<option value="">student1</option>
<option value="">student2</option>
</select>

Initially apply a hidden class (with display: none styling) to the second select list and then on the change of value (indicating a choice has been made) in the first select - remove the hidden class.
EDIT - as as suggested by #HerrSerker - the event listener is now in the JS as opposed to inline in the HTML.
Note that each select list has a selected disabled option - to allow for a blank option rather than the first option selected by default.
// add event listener for change of class select list
document.querySelector('select[name="class"]')
.addEventListener('change', updateStudent)
//function to remove the hidden class and styling of the second select list
function updateStudent() {
var el = document.querySelector('select[name="student"].hidden');
el.classList.remove('hidden')
}
select[name="student"].hidden {
display:none
}
<select name="class">
<option disabled selected></option>
<option value="">class1</option>
<option value="">class2</option>
</select>
<select name="student" class="hidden">
<option disabled selected></option>
<option value="">student1</option>
<option value="">student2</option>
</select>

SELECT control, how to set that what you want to show

I have some issue with this:
<select name="whatever">
<option value="pizza">pizza</option>
<option value="pasta">pasta</option>
<option value="sandwich">sandwich</option>
<option value="cheese">cheese</option>
</select>
Select control always when i "run" it show me as first in drop-down menu a pizza and that mean a pizza is selected by default. So, how i can change this if i want to post cheese to be a default(current active in drop-down)
This down is just a example how i want to work my select, you see down a placeholder=5 , that mean this number control will by default use a 5 and i want to do the similar thing with my select control.
<input type='number' placeholder=5 min=0 max=10 step=1>
Thank you!

You simply just put the attribute of selected on to the option you want as your default.
You can use a JavaScript function to get the value from your table and assign this value as the selected option of the drop-down. The options for a select drop-down are identified by an index starting at 0.
In the demo below, I've used buttons to call the JS function. Click on the button to change the selected option:
var sel = document.getElementsByName("whatever")[0];
function defaultOption(option) {
sel.options[option].selected = 'selected';
}
<button onClick="defaultOption(0)">pizza</button>
<button onClick="defaultOption(1)">pasta</button>
<button onClick="defaultOption(2)">sandwich</button>
<button onClick="defaultOption(3)">cheese</button>
</br>
</br>
<select name="whatever">
<option value="pizza">pizza</option>
<option value="pasta">pasta</option>
<option value="sandwich">sandwich</option>
<option value="cheese" selected>cheese</option>
</select>

Selected Value in dropdownList using Jquery does not appear after set it

I have a problem with asp:dropdownlist when I try to change selected value to some thing using jquery after set the value, dropdownlist shows me last value and does not update to new selected value that have been set by me.
I try it(my html code)
<select name="ctl00$cphMain$ddlBankList" id="ddlBankList">
<option value="2">a</option>
<option value="67">b</option>
<option value="85">c</option>
<option value="175">d</option>
<option value="84">e</option>
<option value="86">f</option>
</select>
and to modify html i use this js
$("#<%=ddlBankList.ClientID%> option:selected").removeAttr("selected");
$("#<%=ddlBankList.ClientID%> option[value='67']").attr('selected', 'true');
But dropdownlist does not Jump to 67 value.

use this
$("#ddlBankList").val(67);
JSFIDDLE

You can use Jquery val function directly for select option in dropdown.
$("#<%=ddlBankList.ClientID%>").val('67');

Change a Select Option value with no id/class

There's this website that I want to change how they display their dropdown menu.
http://i.stack.imgur.com/Wu718.jpg
I wanted to make it so that the default value is "Items for Sale", instead of "Forum Topics"
Here's their source code.
<select name="sec" style="margin-top:5px;width:138px;">
<option value="topics">Forum Topics</option>
<option value="s">Items for Sale</option>
<option value="b">Want to Buys</option>
<option value="users">Members</option>
</select>
Since I don't really care about how it looks, I just want to change the value="topics" to value="s" even without changing the texts.
I've read some tutorials, but they mostly use IDs and Classes as a selector, in this case, how do I target this Select from many other in their website and change the value.

You can use:
$('select[name=sec]').val('s');
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.0.3/jquery.min.js"></script>
<select name="sec" style="margin-top:5px;width:138px;">
<option value="topics">Forum Topics</option>
<option value="s">Items for Sale</option>
<option value="b">Want to Buys</option>
<option value="users">Members</option>
</select>
I think this is what you're describing in the comments below:
var dropdown = $('select[name=sec]');
// change the s option to items
dropdown.find('option[value=s]').attr('value', 'items');
// change the topics option to s
dropdown.find('option[value=topics]').attr('value', 's');
// change the dropdown's value to s
// (first option should continue to be selected because its value is now s)
dropdown.val('s');
// (this is for demo purposes only)
dropdown.after($("<div>").text("New HTML is: " + dropdown[0].outerHTML));
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.0.3/jquery.min.js"></script>
<select name="sec" style="margin-top:5px;width:138px;">
<option value="topics">Forum Topics</option>
<option value="s">Items for Sale</option>
<option value="b">Want to Buys</option>
<option value="users">Members</option>
</select>

You can use the name or any other attribute.
for css
select[name="sec"]
or jquery
$('select[name="sec"]').

DEMO inspect element from your browser to see the changes
you can select a select dropdown list with select[name=sec] and select the first option with option:first
$('select[name=sec] option:first').val('s');
and if you need to change any of options just use .eq()
$('select[name=sec] option').eq(0).val('s'); // eq(0) for the first option element . eq(1) for the second option element ...

If you want to make selected an other option use this code:
$('select[name="sec"]').find('option:selected').removeAttr('selected');
$('select[name="sec"]').find('option[value="s"]').attr('selected','selected');
This script removes the default selection (the first option) and select the option which has "s" value. For the Demo:
$('select[name="sec"]').find('option:selected').removeAttr('selected');
$('select[name="sec"]').find('option[value="s"]').attr('selected','selected');
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.0.3/jquery.min.js"></script>
<select name="sec" style="margin-top:5px;width:138px;">
<option value="topics">Forum Topics</option>
<option value="s">Items for Sale</option>
<option value="b">Want to Buys</option>
<option value="users">Members</option>
</select>
You have to find this element in the DOM. For this you should find the first parent container element of the which has ID or CLASS attribute. From that element you can create a search for the element what you want by using the .find() method.
If there're more element which has name attribute with "sec" value you should build a chain of find which separate that you want. For that you can use these function templates:
$(#CONTAINER_ID).find(.SUBCONTAINER_CLASS).find(ELEMENT_TYPE);
$(#CONTAINER_ID).find(SUBCONTAINER_TYPE).find(OTHER_SUBCONTAINER_TYPE:eq(X));

Javascript: Onclick Set Dropdown Menu Checked Value

UPDATE: I was trying lots of different methods for doing this and none of them worked... until... I changed my dropdown menu name from (date-range) to (dateRange) removing the (-), sorry for wasting time!
I have a search form and a custom reset form button, which resets all the values in the form. I now have a dropdown menu and when the reset button is pressed, I want the first option to be selected.
This is my form:
<select name="date-range" id="date-range">
<option value="Any">Any date</option>
<option value="Today">Today</option>
<option value="Yesterday">Yesterday</option>
<option value="1 Week">Within 1 Week</option>
<option value="1 Month">Within 1 Month</option>
<option value="3 Months">Within 3 Months</option>
<option value="6 Months">Within 6 Months</option>
<option value="1 Year">Within 1 Year</option>
</script>
... and this is my javascript function that now needs to select the first dropdown value "Any".
function resetSearchForm()
{
document.searchFrm.searchStr.value='';
document.searchFrm.vertical.checked = true;
document.searchFrm.horizontal.checked = true;
** dropdown select first **
}
What is the proper way to do this? Any help gratefully received :)

This will work:
document.getElementById('date-range').selectedIndex = 0;
Example can be found here:
http://jsfiddle.net/yPmmG/3/

No javascript required, just add the selected attribute to the first option. That's what the attribute is for.
<option selected value="Any">Any date</option>
It is recommended that all select elements have one option with the selected attribute, that way there is always one selected by default. It will be the selected option when the page first loads and if the form is reset.