Develop Reference

Show/hide element according to the selected option

I want to hide the speech response element, if the user selects the Tamil language from the drop down, but if the user selects English, the speech response element should be hidden.
It doesn't work, I don't know why. Please, give me a suggestion on what's wrong with my code.
Here is my code:
function Speech(say) {
if ('speechSynthesis' in window && talking) {
$('#clitamilhide').hide();
var utterance = new SpeechSynthesisUtterance(say);
speechSynthesis.speak(utterance);
}
}
var msg = new SpeechSynthesisUtterance(ans);
window.speechSynthesis.speak(msg);
<select name="language_" id="langu" class="selectpicker form-control form-control-sm" style="width: 300px; margin-top: 125px;">
<option value="English">
English
</option>
<option value="Tamil">
Tamil
</option>
</select>
In line
var msg = new SpeechSynthesisUtterance(ans);
the backend response will be used and this response goes to the speech() function responding an output as voice.
The main problem is I want to hide the Tamil option tag value inside the function speech(say).

Based on your description (if I got it right), here's a sample you can customize according to your needs.
Change the select tag's option and you'll see, that the sample hides/shows the example element according to the currently selected option.
Quick rundown:
When the user runs your site/web app, we check the currently selected option, if it's English, we are okay, if it's not, we hide the "speech response" element (whatever element will be your final implementation)
An event listener will be also attached to the select tag to detect, when the user changes the current option. If it's English, again, we show the "speech response", if it's not, we're gonna hide it.
// hides the speech response
function showSpeechResponse() {
$('.response').show();
}
// showes the speech response
function hideSpeechResponse() {
$('.response').hide();
}
// checks what's the currently selected option
function checkSelectedOption() {
var element = $('.selectpicker');
switch ($(element).val()) {
case 'English':
showSpeechResponse();
break;
case 'Tamil':
hideSpeechResponse();
break;
}
}
// check the initially selected option
checkSelectedOption();
// when the user selects another option, check the selected option
$('.selectpicker').on('change', checkSelectedOption);
/* your own code here ...
function speech(say) {
if ('speechSynthesis' in window && talking) {
$('#clitamilhide').hide();
var utterance = new SpeechSynthesisUtterance(say);
speechSynthesis.speak(utterance);
}
}
var ans = 'The answer';
var msg = new SpeechSynthesisUtterance(ans);
window.speechSynthesis.speak(msg);
*/
.selectpicker {
/*margin-top: 125px;*/
width: 300px;
}
.response {
margin-top: 15px
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select name="language_" id="langu" class="selectpicker form-control form-control-sm">
<option value="English">English</option>
<option value="Tamil" >Tamil</option>
</select>
<div class="response">Speech Response</div>
Note
I hope you wanted something like this, at least a starting point to use, if I'm mistaken, please, tell me and we're gonna figure out a better solution.

Wrong display of Select Option Tag in Google Chrome [duplicate]

I've realized that Chrome, it seems, will not allow me to hide <option> in a <select>. Firefox will.
I need to hide the <option>s that match a search criteria. In the Chrome web tools I can see that they are correctly being set to display: none; by my JavaScript, but once then <select> menu is clicked they are shown.
How can I make these <option>s that match my search criteria NOT show when the menu is clicked?

For HTML5, you can use the 'hidden' attribute.
<option hidden>Hidden option</option>
It is not supported by IE < 11. But if you need only to hide a few elements, maybe it would be better to just set the hidden attribute in combination with disabled in comparison to adding/removing elements or doing not semantically correct constructions.
<select>
<option>Option1</option>
<option>Option2</option>
<option hidden>Hidden Option</option>
</select>
Reference.

You have to implement two methods for hiding. display: none works for FF, but not Chrome or IE. So the second method is wrapping the <option> in a <span> with display: none. FF won't do it (technically invalid HTML, per the spec) but Chrome and IE will and it will hide the option.
EDIT: Oh yeah, I already implemented this in jQuery:
jQuery.fn.toggleOption = function( show ) {
jQuery( this ).toggle( show );
if( show ) {
if( jQuery( this ).parent( 'span.toggleOption' ).length )
jQuery( this ).unwrap( );
} else {
if( jQuery( this ).parent( 'span.toggleOption' ).length == 0 )
jQuery( this ).wrap( '<span class="toggleOption" style="display: none;" />' );
}
};
EDIT 2: Here's how you would use this function:
jQuery(selector).toggleOption(true); // show option
jQuery(selector).toggleOption(false); // hide option
EDIT 3: Added extra check suggested by #user1521986

I would suggest that you do not use the solutions that use a <span> wrapper because it isn't valid HTML, which could cause problems down the road. I think the preferred solution is to actually remove any options that you wish to hide, and restore them as needed. Using jQuery, you'll only need these 3 functions:
The first function will save the original contents of the select. Just to be safe, you may want to call this function when you load the page.
function setOriginalSelect ($select) {
if ($select.data("originalHTML") == undefined) {
$select.data("originalHTML", $select.html());
} // If it's already there, don't re-set it
}
This next function calls the above function to ensure that the original contents have been saved, and then simply removes the options from the DOM.
function removeOptions ($select, $options) {
setOriginalSelect($select);
$options.remove();
}
The last function can be used whenever you want to "reset" back to all the original options.
function restoreOptions ($select) {
var ogHTML = $select.data("originalHTML");
if (ogHTML != undefined) {
$select.html(ogHTML);
}
}
Note that all these functions expect that you're passing in jQuery elements. For example:
// in your search function...
var $s = $('select.someClass');
var $optionsThatDontMatchYourSearch= $s.find('options.someOtherClass');
restoreOptions($s); // Make sure you're working with a full deck
removeOptions($s, $optionsThatDontMatchYourSearch); // remove options not needed
Here is a working example: http://jsfiddle.net/9CYjy/23/

Ryan P's answer should be changed to:
jQuery.fn.toggleOption = function (show) {
$(this).toggle(show);
if (show) {
if ($(this).parent('span.toggleOption').length)
$(this).unwrap();
} else {
**if ($(this).parent('span.toggleOption').length==0)**
$(this).wrap('<span class="toggleOption" style="display: none;" />');
}
};
Otherwise it gets wrapped in too many tags

Select inputs are tricky in this way. What about disabling it instead, this will work cross-browser:
$('select').children(':nth-child(even)').prop('disabled', true);
This will disable every-other <option> element, but you can select which ever one you want.
Here is a demo: http://jsfiddle.net/jYWrH/
Note: If you want to remove the disabled property of an element you can use .removeProp('disabled').
Update
You could save the <option> elements you want to hide in hidden select element:
$('#visible').on('change', function () {
$(this).children().eq(this.selectedIndex).appendTo('#hidden');
});
You can then add the <option> elements back to the original select element:
$('#hidden').children().appendTo('#visible');
In these two examples it's expected that the visible select element has the id of visible and the hidden select element has the id of hidden.
Here is a demo: http://jsfiddle.net/jYWrH/1/
Note that .on() is new in jQuery 1.7 and in the usage for this answer is the same as .bind(): http://api.jquery.com/on

The toggleOption function is not perfect and introduced nasty bugs in my application. jQuery will get confused with .val() and .arraySerialize()
Try to select options 4 and 5 to see what I mean:
<select id="t">
<option value="v1">options 1</option>
<option value="v2">options 2</option>
<option value="v3" id="o3">options 3</option>
<option value="v4">options 4</option>
<option value="v5">options 5</option>
</select>
<script>
jQuery.fn.toggleOption = function( show ) {
jQuery( this ).toggle( show );
if( show ) {
if( jQuery( this ).parent( 'span.toggleOption' ).length )
jQuery( this ).unwrap( );
} else {
jQuery( this ).wrap( '<span class="toggleOption" style="display: none;" />' );
}
};
$("#o3").toggleOption(false);
$("#t").change(function(e) {
if($(this).val() != this.value) {
console.log("Error values not equal", this.value, $(this).val());
}
});
</script>

Simple answer: You can't. Form elements have very limited styling capabilities.
The best alternative would be to set disabled=true on the option (and maybe a gray colour, since only IE does that automatically), and this will make the option unclickable.
Alternatively, if you can, completely remove the option element.

// Simplest way
var originalContent = $('select').html();
$('select').change(function() {
$('select').html(originalContent); //Restore Original Content
$('select option[myfilter=1]').remove(); // Filter my options
});

Since you're already using JS, you could create a hidden SELECT element on the page, and for each item you are trying to hide in that list, move it to the hidden list. This way, they can be easily restored.
I don't know a way offhand of doing it in pure CSS... I would have thought that the display:none trick would have worked.

You should remove them from the <select> using JavaScript. That is the only guaranteed way to make them go away.

!!! WARNING !!!
Replace the second "IF" by "WHILE" or doesn't work !
jQuery.fn.toggleOption = function( show ) {
jQuery( this ).toggle( show );
if( show ) {
while( jQuery( this ).parent( 'span.toggleOption' ).length )
jQuery( this ).unwrap( );
} else {
jQuery( this ).wrap( '<span class="toggleOption" style="display: none;" />' );
}
};

this one seems to work for me in chrome
$("#selectid span option").unwrap();
$("#selectid option:not([filterattr=filtervalue])").wrap('<span/>');

Simply use option[value=your-value]{display:none;}
This works fine in Chrome, at least in 2022, as well as in safari and FF.

Modern solution is simply apply CSS hidden like:
<option value="" style="display:none;">Select Item</option>
Or with a class
<option value="" class="hidden">Please select</option>
Note in class case, add css like
.hidden {
display: none;
}

Late to the game, but most of these seem quite complicated.
Here's how I did it:
var originalSelect = $('#select-2').html();
// filter select-2 on select-1 change
$('#select-1').change(function (e) {
var selected = $(this).val();
// reset select ready for filtering
$('#select-2').html(originalCourseSelect);
if (selected) {
// filter
$('#select-2 option').not('.t' + selected).remove();
}
});
markup of select-1:
<select id='select-1'>
<option value=''>Please select</option>
<option value='1'>One</option>
<option value='2'>Two</option>
</select>
markup of select-2:
<select id='select-2'>
<option class='t1'>One</option>
<option class='t2'>Two</option>
<option>Always visible</option>
</select>

Simply, this can achieved by HTML too.
<select>
<option value="" disabled selected hidden>Please Choose</option>
<option value="0">hii</option>
<option value="1">hello</option>
</select>

2022 Answer Summary And Cross-Browser Solution
Currently, these methods do not work on Safari:
visibility: hidden
display: block
hidden attribute
So none of proposed solutions here using these methods works on Safari, so they can not be accepted.
Solution
The solution is to keep special options in an array, and hide/restore them on-demand. For example to show/hide day selection based on year/month selection:
When you initialize your component:
const tailDayOptions = [];
const saveTailDayOptions = () => {
const daySelector = document.querySelector('#daySelector');
for (let day = 29; day <= 31; day++) {
tailDayOptions[day - 1] = daySelector.querySelector(`option[value='${day - 1}']`);
}
}
When a user changes year or month:
for (let day = 29; day <= 31; day++) {
if (day <= daysInMonth) {
daySelector.appendChild(tailDayOptions[day - 1])
} else {
const dayOption = daySelector.querySelector(`option[value='${day - 1}']`);
if (dayOption) {
daySelector.removeChild(dayOption);
}
}
}
How does it work
It saves options for day 29,30 and 31 to a tailDayOptions array
When user changes the year or month, daysInMonth are calculated
If a given day (e.g. 29th) is not present in a given year-month and it is available in the select options, it gets removed from there
If a given day is available in a given year-month it gets re-added to the select from the tailDayOptions array
Compatibility
Compatible with Firefox, Chrome and Safari. Should be compatible with all other browsers.

Drop down list width fit selected item text

Is there a way in javascript/jquery or css to make html <select>/#Html.DropDownList auto width so it fits currently selected item, I tried with diplay:inline-block and width:auto but width always seems to fit largest item on list?

My answer is similar to D3mon-1stVFW's, but instead uses a hidden drop-down to set the width on dynamically. As long as you use the same styling for your hidden and "real" one, it should account for different font sizes, decoration, etc. Here's the HTML:
<!-- this is our hidden "template" drop-down that we'll
use to determine the size of our "real" one -->
<select id="template" style="display:none;">
<option id="templateOption"></option>
</select>
<!-- this is our "real" template that will be re-sized -->
<select id="sel">
<option>Short</option>
<option>Really, Really, Really Long</option>
</select>​
And the Javascript:
function setSelectWidth() {
var sel = $('#sel');
$('#templateOption').text( sel.val() );
// for some reason, a small fudge factor is needed
// so that the text doesn't become clipped
sel.width( $('#template').width() * 1.03 );
}
$(document).ready( function() {
setSelectWidth();
$('#sel').change( function() {
setSelectWidth();
} );​
});
JSFiddle here: http://jsfiddle.net/kn9DF/1/

Variation on #Ethan Brown's answer, with the .val() corrected to .text() and a dynamically-created select so your page isn't polluted:
HTML:
<select id="sel">
<option>Short</option>
<option>Really, Really, Really Long</option>
</select>​
JS:
function setSelectWidth(selector) {
var sel = $(selector);
var tempSel = $("<select style='display:none'>")
.append($("<option>").text(sel.find("option:selected").text()));
tempSel.appendTo($("body"));
sel.width(tempSel.width());
tempSel.remove();
}
$(function() {
setSelectWidth("#sel");
$("#sel").on("change", function() {
setSelectWidth($(this));
});
});
Fiddle:
http://jsfiddle.net/kn9DF/242/
Tested on Chrome 39, FF 36, IE 11.

Here's a generic jQuery function you can drop into any page. It immediately resizes all selectors and ensures they will be resized when they are changed.
function setSelectWidth() {
var $yardstick = $('<select><option>' + $(this).val() + '</option></select>')
$yardstick.css({display: 'none'}).appendTo('body');
var fudge = 1.03; // need a little more to avoid clipping for some reason
$(this).width( fudge * $yardstick.width() );
$yardstick.remove();
}
function initSelectors() {
$('select').each(function() {
setSelectWidth.apply(this);
}).one('change', function() {
setSelectWidth.apply(this);
});
}
initSelectors();
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<!-- examples -->
<select id="example-1">
<option>Short</option>
<option>Really, Really, Really Long</option>
</select>
<select id="example-2">
<option>Tiny</option>
<option>A bit bigger</option>
<option>Huuuuuuuuuuuuuuuuuuuuge</option>
</select>
The script is forked from Ethan and Ian's answers. The initSelectors function does need to be re-called if you add a selector, but it uses jQuery one so it can be safely called multiple times if previous selectors remain on the page.

Use this sample I wrote. Use the same when you create the list, just get the default selected and set it in the span and get its width.
<script>
function newSelected(ele){
document.getElementById('jsize').innerHTML = ele.value;
document.getElementById('selectList').style.width = ($(jsize).width()+30)+'px';
}
</script>
<span id="jsize" style="display:none"></span><br />
<select id="selectList" onchange="newSelected(this);">
<option>small item</option>
<option>a really big long item</option>
</select>
​
see http://jsfiddle.net/39ffp/2/ it can be tweaked

How to avoid the need for ctrl-click in a multi-select box using Javascript?

I thought this would be a simple hack, but I've now been searching for hours and can't seen to find the right search term. I want to have an ordinary multiple select box (<select multiple="multiple">) except I don't want the user to have to hold down the control key to make multiple selections.
In other words, I want a left click to toggle the <option> element that's under the cursor without changing any of the others. In other other words, I want something that looks like a combo list box but behaves like a group of check boxes.
Can anybody suggest a simple way to do this in Javascript? Thanks.

Check this fiddle: http://jsfiddle.net/xQqbR/1022/
You basically need to override the mousedown event for each <option> and toggle the selected property there.
$('option').mousedown(function(e) {
e.preventDefault();
$(this).prop('selected', !$(this).prop('selected'));
return false;
});
For simplicity, I've given 'option' as the selector above. You can fine tune it to match <option>s under specific <select> element(s). For ex: $('#mymultiselect option')

Had to solve this problem myself and noticed the bugged behavior a simple interception of the mousedown and setting the attribute would have, so made a override of the select element and it works good.
jsFiddle: http://jsfiddle.net/51p7ocLw/
Note: This code does fix buggy behavior by replacing the select element in the DOM. This is a bit agressive and will break event handlers you might have attached to the element.
window.onmousedown = function (e) {
var el = e.target;
if (el.tagName.toLowerCase() == 'option' && el.parentNode.hasAttribute('multiple')) {
e.preventDefault();
// toggle selection
if (el.hasAttribute('selected')) el.removeAttribute('selected');
else el.setAttribute('selected', '');
// hack to correct buggy behavior
var select = el.parentNode.cloneNode(true);
el.parentNode.parentNode.replaceChild(select, el.parentNode);
}
}
<h4>From</h4>
<div>
<select name="sites-list" size="7" multiple>
<option value="site-1">SITE</option>
<option value="site-2" selected>SITE</option>
<option value="site-3">SITE</option>
<option value="site-4">SITE</option>
<option value="site-5">SITE</option>
<option value="site-6" selected>SITE</option>
<option value="site-7">SITE</option>
<option value="site-8">SITE</option>
<option value="site-9">SITE</option>
</select>
</div>

techfoobar's answer is buggy, it unselects all options if you drag the mouse.
Sergio's answer is interesting, but cloning and removing events-bound to a dropdown is not a nice thing.
Try this answer.
Note: Doesn't work on Firefox, but works perfectly on Safari/Chrome/Opera. (I didn't test it on IE)
EDIT (2020)
After 5 years since my original answer, I think best practice here is to replace the dropdown with checkboxes. Think about it, that's the main reason why checkboxes exist in the first place, and it works nicely with old browsers like IE & modern mobiles without any custom JS to handle all the wacky scenarios.

Necromancing.
The selected answer without jQuery.
Also, it missed setting the focus when an option is clicked, because you have to do this yourself, if you write e.preventDefault...
Forgetting to do focus would affect CSS-styling, e.g. bootstrap, etc.
var options = [].slice.call(document.querySelectorAll("option"));
options.forEach(function (element)
{
// console.log("element", element);
element.addEventListener("mousedown",
function (e)
{
e.preventDefault();
element.parentElement.focus();
this.selected = !this.selected;
return false;
}
, false
);
});

I had same problem today, generally the advice is to use a list of hidden checkboxes and emulate the behavior via css, in this way is more easy to manage but in my case i don't want to modify html.
At the moment i've tested this code only with google chrome, i don't know if works with other browser but it should:
var changed;
$('select[multiple="multiple"]').change(function(e) {
var select = $(this);
var list = select.data('prevstate');
var val = select.val();
if (list == null) {
list = val;
} else if (val.length == 1) {
val = val.pop();
var pos = list.indexOf(val);
if (pos == -1)
list.push(val);
else
list.splice(pos, 1);
} else {
list = val;
}
select.val(list);
select.data('prevstate', list);
changed = true;
}).find('option').click(function() {
if (!changed){
$(this).parent().change();
}
changed = false;
});
Of course suggestions are welcome but I have not found another way

Reusable and Pure JavaScript Solution
const multiSelectWithoutCtrl = ( elemSelector ) => {
let options = document.querySelectorAll(`${elemSelector} option`);
options.forEach(function (element) {
element.addEventListener("mousedown",
function (e) {
e.preventDefault();
element.parentElement.focus();
this.selected = !this.selected;
return false;
}, false );
});
}
multiSelectWithoutCtrl('#mySelectInput') /* Can use ID or Class */
option {
font-size: 20px;
padding: 10px 20px;
}
<select multiple id="mySelectInput" class="form-control">
<option>🍎 Apple</option>
<option>🍌 Banana</option>
<option>🍍 Pineapple</option>
<option>🍉 Watermelon</option>
</select>

How can you programmatically tell an HTML SELECT to drop down (for example, due to mouseover)?

How can you programmatically tell an HTML select to drop down (for example, due to mouseover)?

This used to actually be possible with HTML+Javascript, despite everywhere else people say it is not, but it was deprecated later on and does not work now.
However, this only worked in Chrome. Read more if you're interested.
According to W3C Working Draft for HTML5, Section 3.2.5.1.7. Interactive Content:
Certain elements in HTML have an activation behavior, which means that the user can activate them. This triggers a sequence of events dependent on the activation mechanism [...] for instance using keyboard or voice input, or through mouse clicks.
When the user triggers an element with a defined activation behavior in a manner other than clicking it, the default action of the interaction event must be to run synthetic click activation steps on the element.
<select> being an Interactive Content, I believed that it is possible to programatically display its <option>s. After a few hours of playing around, I discovered that using document.createEvent() and .dispatchEvent() works.
That said, demo time. Here is a working Fiddle.
// <select> element displays its options on mousedown, not click.
showDropdown = function(element) {
var event;
event = document.createEvent('MouseEvents');
event.initMouseEvent('mousedown', true, true, window);
element.dispatchEvent(event);
};
// This isn't magic.
window.runThis = function() {
var dropdown = document.getElementById('dropdown');
showDropdown(dropdown);
};
<select id="dropdown">
<option value="Red">Red</option>
<option value="Green">Green</option>
<option value="Blue">Blue</option>
</select>
<br>
<button id="fire" type="button" onclick="runThis()">Show dropdown items</button>​
If anyone finds a way to do the same but not in Chrome, please feel free to modify this fiddle.
​

Xavier Ho's answer is covering how to solve the issue in most browsers currently out there. But, it's good practice 'not to dispatch/modify' events by JavaScript anymore. (Like, mousedown in this case)
From version 53+, Google Chrome will not perform default action for un-trusted events. Such as events created or modified by script, or dispatched via dispatchEvent method. This change is for aligning with Firefox and IE which I think already not performing the action.
For testing purposes, Fiddle provided Xavier's answer won't work in chrome 53+. (I don't test it FF and IE).
Links for reference:
https://www.chromestatus.com/features/5718803933560832
https://www.chromestatus.com/features/6461137440735232
And initMouseEvent is also deprecated

This is the closest I could get, change the size of the element onmouseover, and restore the size onmouseout:
<select onMouseOut="this.size=1;" onMouseOver="this.size=this.length;">
<option>1</option>
<option>2</option>
<option>3</option>
<option>4</option>
<option>5</option>
</select>

I have this same problem and the easier way I found to solve this was with HTML and CSS.
First, make you <select> transparent (opacity: 0;). Then, place your button over the <select>. The click over the button will be caught by the <select> component.
select{
opacity: 0;
position: absolute;
}
select:hover~button {
background: orange;
}
div * {
width: 100px;
}
<div>
<select>
<option>option 1</option>
<option>option 2</option>
<option>option 3</option>
</select>
<button>click</button>
</div>

You can't do this with a HTML select tag, but you can do it with JavaScript and HTML. There are variety of existing controls that do this - for instance, the "suggest" list attached to the SO "interesting/ignored tag" entry, or Gmail's lookup for email adresses.
There are many JavaScript+HTML controls that provide this capability--look for autocomplete controls for ideas.
See this link for the Autocomplete control...http://ajaxcontroltoolkit.codeplex.com/

I think this is no longer possible in Chrome.
It seems version 53 of chrome disables this functionality as stated by Asim K T.
According to the spec
http://www.w3.org/TR/DOM-Level-3-Events/#trusted-events
Trusted Events should not fire the default action (except click
event).
They have however enabled it in webview, but I have not tested this.
We have found that some webviews are using fastclick inside them and
due to a risk of breakage we are going to allow mousedown on selects
even if they are untrusted.
And in this discussion the idea to let developers open a dropdown programatically is abandoned.

If any one is still looking for this :
<select id="dropdown">
<option value="Red">Red</option>
<option value="Green">Green</option>
<option value="Blue">Blue</option>
</select>
<br>
<button id="fire" type="button" >Show dropdown items</button>
Javascript:
var is_visible=false;
$(document).ready(function(){
$('#fire').click(function (e) {
var element = document.getElementById('dropdown');
if(is_visible){is_visible=false; return;}
is_visible = true;
var event;
event = document.createEvent('MouseEvents');
event.initMouseEvent('mousedown', true, true, window);
element.dispatchEvent(event);
/* can be added for i.e. compatiblity.
optionsSelect.focus();
var WshShell = new ActiveXObject("WScript.Shell");
WshShell.SendKeys("%{DOWN}");
*/
e.stopPropagation();
return false;
});
$(document).click(function(){is_visible=false; });
});
Update:
One till there is no perfect solution to this problem, But you can try to avoid this scenario. Why do you want to do this. i was wondering for a solution few months back to make a select plugin for mobile devices
https://github.com/HemantNegi/jquery.sumoselect
Finally ended up with masking the custom div (or any other element) with a transparent select element, so that it can directly interacts with user.

Here's the best way I found. NOTE It only works with IE on Windows and your web would probably need to be in a secure zone - because we access the shell. The trick is that ALT-Down Arrow is a shortcut key to open a select drop down.
<button id="optionsButton" style="position:absolute;top:10px;left:10px;height:22px;width:100px;z-index:10" onclick="doClick()">OPTIONS</button>
<select id="optionsSelect" style="position:absolute;top:10px;left:10px;height:20px;width:100px;z-index:9">
<option>ABC</option>
<option>DEF</option>
<option>GHI</option>
<option>JKL</option>
</select>
<script type="text/javascript">
function doClick() {
optionsSelect.focus();
var WshShell = new ActiveXObject("WScript.Shell");
WshShell.SendKeys("%{DOWN}");
}
</script>

Stop thinking that one thing is impossible, nothing is impossible to do, when you want to do.
Use this expand JS function created by a guy.
http://code.google.com/p/expandselect/
Include this JS and just call that passing the param as your select id, like that:
ExpandSelect(MySelect)

If anyone is still looking for this,
This is how I solved it.
This is a solution based on the fact that the selection looks like it is expanded when the size in increased. We can increase size to make it look expanded. And reduce to make it seem closed. This way we can handle most use-cases by just having focus and blur listeners.
Select element needs to be absolutely positioned because increasing size will increase vertical height of element. If you have elements below, they will be pushed down if this is not done.
I have a wrapper code, that wraps the element and provides open and close methods.
Check this fiddle for usage: https://jsfiddle.net/10ar2ebd/16/
var SelectionWrapper = function(element, maxSize, selectCb) {
var preventDefault = function(e) {
e.preventDefault();
e.stopPropagation();
}
var isOpen = false;
var open = function() {
if (!isOpen) {
element.size = maxSize;
// Remove prevent default so that user will be able to select the option
// Check why we prevent it in the first place below
element.removeEventListener('mousedown', preventDefault);
// We focus so that we can close on blur.
element.focus();
isOpen = true;
}
};
var close = function() {
if (isOpen) {
element.size = 1;
// Prevent default so that the default select box open behaviour is muted.
element.addEventListener('mousedown', preventDefault);
isOpen = false;
}
};
// For the reason above
element.addEventListener('mousedown', preventDefault);
// So that clicking elsewhere closes the box
element.addEventListener('blur', close);
// Toggle when click
element.addEventListener('click', function(e) {
if (isOpen) {
close();
// Call ballback if present
if(selectCb) {
selectCb(element.value);
}
} else {
open();
}
});
return {
open: open,
close: close
};
};
// Usage
var selectionWrapper = SelectionWrapper(document.getElementById("select_element"), 7, function(value) {
var para = document.createElement("DIV");
para.textContent = "Selected option: " + value;
document.getElementById("result").appendChild(para);
});
document.getElementById("trigger").addEventListener('click', function() {
selectionWrapper.open();
});

Here is the solution on https://jsfiddle.net/NickU/ahLy83mk/50/
It uses size="x" to open the dropdown while maintaining the dropdown and parent positions. The code also uses CSS styles to hide the right scroll area when it is not needed. I modified the code I found on stackoverflow, fixed the problems and added styling.
HTML:
<div>DIV example: <select id="dropdownDiv">
<option value="Alpha">Alpha</option>
<option value="Beta">Beta</option>
<option value="Gamma">Gamma</option>
</select>
</div>
<table id='tab1'>
<tr><td>Empty Cell</td></tr>
<tr><td> <select id="dropdown1">
<option value="Red">Red</option>
<option value="Green">Green</option>
<option value="Blue">Blue</option>
</select>
</td>
<tr><td><select id="dropdown2">
<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="15">1</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></select>
</td></tr>
<tr><td>Empty Cell</td></tr></table>
<br><button id="fire" type="button" onclick="openDropdown('dropdownDiv', this)" >Show dropdownDiv items</button>
<button id="fire" type="button" onclick="openDropdown('dropdown1', this)" >Show dropdown1 items</button>
<button id="fire" type="button" onclick="openDropdown('dropdown2', this)" >Show dropdown2 items</button>
JavaScript:
var lastClosedElem = null;
var maxItemsInDropDown = 12;
function openDropdown(elementId, opener)
{
if (lastClosedElem !== null && lastClosedElem === opener)
{
lastClosedElem = null;
return;
}
lastClosedElem = opener;
function down()
{
var $this = $(this);
var td = $this.closest('td,div');
if (td && td.length > 0)
td.height(td.height());
var pos = $this.offset();
var len = $this.find("option").length;
if (len > 1 && len < maxItemsInDropDown)
{
$this.addClass('no-scroll');
$this.addClass('noArrow');
}
else if (len > maxItemsInDropDown)
{
len = maxItemsInDropDown;
}
$this.css("position", "absolute");
var _zIndex = $this.css("zIndex");
if (!_zIndex)
_zIndex = 'auto';
$this.attr("_zIndex", _zIndex);
$this.css("zIndex", 9999);
$this.attr("size", len); // open dropdown
$this.unbind("focus", down);
$this.focus();
}
var up = function()
{
var $this = $(this);
$this.css("position", "static");
$this.attr("size", "1");
$this.removeClass('no-scroll');
$this.removeClass('noArrow');
var _zIndex = $this.attr("zIndex");
if (_zIndex)
{
$this.css("zIndex", _zIndex);
}
$this.unbind("blur", up);
$this.unbind("click", upClick);
$this.focus();
}
function upClick(e)
{
up.call(this);
lastClosedElem = null;
}
$("#" + elementId).focus(down).blur(up).click(upClick).trigger('focus');
}
CSS:
.no-scroll { cursor: pointer;}
.no-scroll::-webkit-scrollbar {display:none;}
.no-scroll::-moz-scrollbar {display:none;}
.no-scroll::-o-scrollbar {display:none;}
.no-scroll::-google-ms-scrollbar {display:none;}
.no-scroll::-khtml-scrollbar {display:none;}
.noArrow {
-webkit-appearance: none;
-moz-appearance: none;
appearance: none;
padding-left: 3px;
padding-right: 3px;
}
/* Cosmetic styles */
#tab1 tbody tr:nth-child(even) > td, div
{ background: linear-gradient( 180deg, #efefef 1%, #eeeeee 15%, #e2e2e2 85%);
}
#tab1 tbody tr td
{ padding: 4px;
}
#tab1
{ border: 1px solid silver;
}

I may be wrong, but I don't believe that is possible with the default select box. You could do something with JS & CSS that achieves the desired result, but not (to my knowledge) the vanilla SELECT.

This is not exactly what you asked for, but I like this solution for its simplicity. In most cases where I am wanting to initiate a dropdown, it is because I'm validating that the user has actually made a selection. I change the size of the dropdown and focus it, which nicely highlights what they've skipped:
$('#cboSomething')[0].size = 3;
$('#cboSomething')[0].focus();

Opening an "HTML select" is possible through some workarounds mentioned in this question and similar ones. However a cleaner way of doing this is to add a select library to your project like "select2" or "chosen".
For instance, opening a select2 programmatically would be as easy as:
$('#target-select').select2('open');

I don't know if I'm fully understanding the question, but to open a dropdown, this simple approach worked for me.
You have an element:
<span onclick="openDropdown();">Open dropdown</span>
You have a dropdown:
<select class="dropdown">
<option value="A">Value A</option>
<option value="B">Value B</option>
<option value="C">Value C</option>
</select>
And with JavaScript you can do the following:
document.querySelector('.dropdown').focus();

let elSelected = null;
function bindSelectClick(el){
if(el.target !== elSelected){
$(elSelected).trigger('blur');
$(document).unbind('click', bindSelectClick)
}
}
$('select.shared_date').on('focus', function (){
// do something
elSelected = this;
$(document).on('click', bindSelectClick)
}).on('blur', function (){
// do something
}).on('change', function (){
// do something
})
Select does not lose focus after its menu is closed.
With a separate function, we check whether the click was on the select or elsewhere. If the elements are not equal, then you can fire some kind of event