Develop Reference

Reset select dropdown base on hierarchy

<script>
function refresh()
{
document.forms[0].submit();
}
</script>
<select name = "firstoption" onChange ="refresh()"></select>
<option value = "">default option</option>
<option value = "1">1</option>
if($_POST['firstoption]!= "")
<select name = "secondoption" onChange ="refresh()"></select>
<option value = "">default option</option>
<option value = "2">2</option>
if($_POST['secondoption]!= "" && $_POST['firstoption]!= "")
<select name = "thirdoption" onChange ="refresh()"></select>
<option value = "">default option</option>
<option value = "3">3</option>
if($_POST['thirdoption]!= "" && $_POST['secondoption]!= "" && $_POST['firstoption]!= "")
<select name = "fourthoption" onChange ="refresh()"></select>
<option value = "">default option</option>
<option value = "4">4</option>
Hi,
I have 6 static dropdowns. (something like this for some reason I am currently having laptop problems so I could not copy and paste the code where I wrote down generic values)
DELETED (NO LONGER AN ISSUE FIX ON MY OWN)
Basically, I need 6 dropdown (all values kept after it s refresh) and when a dropdown values changes all of the dropdowns below it get reset.
EDIT:
I am looking for code to reset select option back to the default select option (base on hierarchy). Once an select option above it gets change. so if select "2" gets change select 3,4,5 6 value should change to default option. If select "4" gets change select 5,6 would be change to default option etc.
I do not want ajax or jQuery. I am looking for a solution with php, javascript, or html. I think the way to approach it is by comparing the previous and new index number of the select option being change
Note the code I provide is sudo code I can not copy and paste code due to current laptop state.
So the answer does not need to use my code.
I just want a php/javascript/html code that has multiple select options (4-6 select with 2 option in each) the other drop down will be disable until the select above get a value. SO option 2-6 will be disable until select 1 is pick then option 3-6 will be disable until a value for option 2 is pick).
If he user changes select 1 option will select 2-6 already have a value. Select 2-6 automatically switches to default option value. and option 3-6 is now disable until user select option for select 2
Also stack overflow does not allow bounty to be given until 24 hours so I can not give bounty until tomorrow around this time.

Some suggestions to facilitate the solution:
Give all your drop-down lists the same class attribute.
Use just one change event handler on a container element (or the whole document), and let the handler find out which select value was changed.
Create a function that, given an index, will clear all dropdowns from that index onwards, and will disable all of those, except the first one (at that index).
Call this function in the event handler, and also at page load, so to initialise the enabled/disabled status of those dropdowns.
Below is how that could work. I removed all HTML that is not necessary for this solution, but of course you may need more HTML attributes for other purposes:
const dropDowns = Array.from(document.querySelectorAll(".option"));
function reset(i) {
for (let other of dropDowns.slice(i)) {
other.selectedIndex = 0;
other.disabled = other !== dropDowns[i];
}
}
document.addEventListener("change", function (e) {
let i = dropDowns.indexOf(e.target);
if (i < 0) return;
// only allow input in next one if current value is not default:
reset(i+(dropDowns[i].selectedIndex > 0));
});
reset(0); // on page load, disable all except first one
<select class="option">
<option>default option</option>
<option>1</option>
<option>2</option>
</select>
<select class="option">
<option>default option</option>
<option>A</option>
<option>B</option>
</select>
<select class="option">
<option>default option</option>
<option>x</option>
<option>y</option>
</select>
<select class="option">
<option>default option</option>
<option>alpha</option>
<option>beta</option>
</select>
More on the following:
reset(i+(dropDowns[i].selectedIndex > 0));
dropDowns[i].selectedIndex will be 0 when the first entry (default) is selected, and a strictly positive number when any other entry is selected. So with > 0 this actually gives true for when a non-default entry is selected, false otherwise.
Now we want to make the next dropdown available only when the current one has a non-default entry selected, i.e. when this > 0 expression is true. By involving that expression in a + operation, we convert that boolean value to a number (0 for false, 1 for true). And so, that whole expression is either i+0 or i+1, depending on whether the current dropdown has the default value selected or not.
By providing that index (i or i+1) to the reset function, we make sure that the effect of selecting the default value or not is just like is needed.

There are many ways to accomplish this. The below should work with any number of select boxes. The code is commented to explain the steps.
<form accept="#" method="POST" id="myform">
<div>
<select name="firstoption">
<option value="">default option</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
</div>
<div>
<select name="secondoption" disabled>
<option value="">default option</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
</div>
<div>
<select name="thirdoption" disabled>
<option value="">default option</option>
<option value="3">3</option>
<option value="4">4</option>
</select>
</div>
<div>
<select name="fourthoption" disabled>
<option value="">default option</option>
<option value="4">4</option>
<option value="5">5</option>
</select>
</div>
<div>
<input type="submit" value="Submit">
</div>
</form>
<script>
//get references to the DOM elements we need
var form = document.getElementById('myform');
var selects = form.querySelectorAll('select');
//register event listeners for each of the select boxes so we know when the value changes
for( let i=0; i<selects.length; i++ ) {
selects[i].addEventListener('change', function(evt) {
//select box "i" has changed
//since the value changed, reset other boxes after to the default value and disable
for( let i2 = (i+1); i2 < selects.length; i2++ ) {
selects[i2].value = "";
selects[i2].disabled = true;
}
//if the value of the changed select box is not the default, enable the next one
if( selects[i].value !== "" && selects[i+1] ) {
selects[i+1].disabled = false;
}
});
}
//catch form submission so we can validate the select boxes
form.addEventListener('submit', function(evt) {
//ensure we have all values before submitting
try {
for( let i=0; i<selects.length; i++ ) {
if( selects[i].value === "" ) {
alert(`Please select an option for box number ${i+1}`);
throw 0;
}
}
}catch(e) {
//error, prevent submission
evt.preventDefault();
return false;
}
//all good, submit
return true;
});
</script>

Load all select with document.querySelectorAll() using an expresion to get elements wich name ends with option, that's what $ do before the equal sign.
Then, in your function, check every select if one is empty, set to default value the next.
// Get all items wich name ends with "option"
let selects = document.querySelectorAll('[name$="option"]');
function refresh() {
// Loop into all selects
selects.forEach((item, index) => {
// Don't do this on last one
if(item.value == '' && index < selects.length - 2)
selects[index + 1].value = ""
});
// Check here the sixthoption value if you need it not empty to submit the form
}
<select name="firstoption" onchange="refresh()">
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<select name="secondoption" onchange="refresh()">
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<select name="thirdoption" onchange="refresh()">
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<select name="fourthoption" onchange="refresh()">
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<select name="fifthoption" onchange="refresh()">
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<select name="sixthoption" onchange="refresh()">
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
Another way using if's:
// Get all items wich name ends with "option"
let selects = document.querySelectorAll('[name$="option"]');
function refresh() {
// 0 = firstoption, 1 = secondoption... 5 = sixthoption
// If value is empty string, set default value for next element too
if(selects[0].value == "") selects[1].value = '';
if(selects[1].value == "") selects[2].value = '';
if(selects[2].value == "") selects[3].value = '';
if(selects[3].value == "") selects[4].value = '';
if(selects[4].value == "") selects[5].value = '';
}
<select name="firstoption" onchange="refresh()">
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<select name="secondoption" onchange="refresh()">
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<select name="thirdoption" onchange="refresh()">
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<select name="fourthoption" onchange="refresh()">
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<select name="fifthoption" onchange="refresh()">
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<select name="sixthoption" onchange="refresh()">
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>

I assume that you not necessarily want to post upon each select change. Instead, let's see this approach:
<select class="fancy-select" id="s-1" name = "firstoption">
<option value = "">default option</option>
<option value = "1">1</option>
</select>
<select class="fancy-select" id="s-2" name = "secondoption">
<option value = "">default option</option>
<option value = "2">2</option>
</select>
<select class="fancy-select" id="s-3" name = "thirdoption">
<option value = "">default option</option>
<option value = "3">3</option>
</select>
<select class="fancy-select" id="s-4" name = "fourthoption">
<option value = "">default option</option>
<option value = "4">4</option>
</select>
<script type="text/javascript">
function myHandler() {
if (!this.value) {
var currentID = parseInt(this.id.substring(2));
for (let i = currentID; i < fancySelects.length; i++) fancySelects[i].value = "";
}
}
var fancySelects = document.querySelectorAll(".fancy-select");
for (let item of fancySelects) item.addEventListener("change", myHandler);
</script>
Fiddle: https://jsfiddle.net/0dfxytpc/1/
You see that despite the claims about Vue JS and jQuery making it easier, Javascript in itself is easy. If you know how to program in Javascript. My understanding is that once default is chosen you intend the subsequent items to be defaulted. If that's not the aim, then I misunderstood the goal.
Now, you can notice that this is pretty repetitive, we can surely make it nicer to appear. Let's generate the select tags on the server:
<?php
for ($index = 1; $index <= 4; $index++) {
?>
<select class="fancy-select" id="s-<?php echo $index; ?>">
<option value="">default option</option>
<option value="<?php echo $index; ?>"><?php echo $index; ?></option>
</select>
<?php
}
?>
<script type="text/javascript">
function myHandler() {
if (!this.value) {
var currentID = parseInt(this.id.substring(2));
for (let i = currentID; i < fancySelects.length; i++) fancySelects[i].value = "";
}
}
var fancySelects = document.querySelectorAll(".fancy-select");
for (let item of fancySelects) item.addEventListener("change", myHandler);
</script>
The code is small and easy to understand. Vue JS and jQuery would just overcomplicate this, they would add dependencies that you do not need. There is a trend of programmers who are less capable to work in Javascript and will argue that doing stuff is easier in Vue JS or jQuery. You can actually measure the power of that trend with the number of downvotes I get. I do not speak against the use of jQuery or Vue JS in general, although, I am not their fan in particular, but when you learn Javascript you should avoid getting dependant of a framework right from the start. As you get comfortable working with Javascript you might decide that Vue JS and jQuery is good for you. I would totally respect that decision, but do not make that decision before you learn Javascript properly.

You could try this:
const selects = document.querySelectorAll(".myoption");
const submit = document.getElementById("mysubmit");
selects.forEach((select, id) => select.addEventListener("change",() => {
const last = id === selects.length - 1;
if(! last) {
selects[id + 1].removeAttribute("disabled");
selects[id + 1].value = "";
}
for(let i = id + (select.selectedIndex ? 2 : 1); i < selects.length; ++i) {
selects[i].value = "";
selects[i].setAttribute("disabled", true);
}
submit.setAttribute("disabled", true);
if(last && select.selectedIndex) submit.removeAttribute("disabled");
}));
<select class="myoption">
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
<select class="myoption" disabled>
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
<select class="myoption" disabled>
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
<select class="myoption" disabled>
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
<select class="myoption" disabled>
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
<select class="myoption" disabled>
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
<input type="submit" id="mysubmit" value="submit" disabled>
Hope this helps.

As already a lot of ways are mentioned, here is what I came up with.
Assign every select a data-name attribute.
Every select would also have a class attribute. This class attribute would possess all previous parents' data-names.
When a particular select value changes, you get the data-name of it and use querySelectorAll to get all those elements who have this data-name in their class and set their values and disability accordingly.
var selects = document.querySelectorAll('select');
selects.forEach(function(select_dropdown){
select_dropdown.addEventListener('change',function(){
var kids = document.querySelectorAll('.' + this.getAttribute('data-name'));
var parent_value = this.value;
kids.forEach(function(child,index){
child.value = "";
if(parent_value == "" || index > 0){
child.setAttribute('disabled','disabled');
}else{
child.removeAttribute('disabled');
}
});
});
});
<select class="" data-name="select_1">
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
<select data-name="select_2" class="select_1" disabled>
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
<select data-name="select_3" class="select_1 select_2" disabled>
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
<select data-name="select_4" class="select_1 select_2 select_3" disabled>
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
<select data-name="select_5" class="select_1 select_2 select_3 select_4" disabled>
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
<select data-name="select_6" class="select_1 select_2 select_3 select_4 select_5" disabled>
<option value="">Default</option>
<option value="1">1</option>
<option value="2">2</option>
</select>

You can add data attribute for each dropdown, that way you can track index of that dropdown, so on change all higher than index apply action..
when option is selected, reset rest of the boxes that are in order.
If previus select box not default, enable next box else disable it
var selects = document.getElementsByClassName("select")
for(var i = 0; i < selects.length; i++){
selects[i].addEventListener('change', function(e){
for(var x = 0; x < selects.length; x++){
//On select, reset selectboxes that commes after
if(Number(e.target.dataset.columns) < x){
selects[x][0].selected = true;
}
//If previus select box not default, enable next box
if(x > 0 && selects[x -1][0].selected != true){
selects[x].disabled = false;
}
//else dissable next box..
else if(x > 0 && selects[x -1][0].selected == true){
selects[x].disabled= true;
}
}
})
}
<select data-columns="0" class="select">
<option value = "">default option</option>
<option value = "1">1</option>
<option value = "1">1</option>
</select>
<select data-columns="1" disabled class="select">
<option value = "">default option</option>
<option value = "2">2</option>
<option value = "1">1</option>
</select>
<select data-columns="2" disabled class="select">
<option value = "">default option</option>
<option value = "3">3</option>
<option value = "1">1</option>
</select>
<select data-columns="3" disabled class="select">
<option value = "">default option</option>
<option value = "4">4</option>
<option value = "1">1</option>
</select>

Hide select options based on previous selections

Is it possible to hide options in a select/dropdown with jQuery based on the user's selection from a previous dropdown e.g:
If user is 8 (Age Select/Dropdown), and chooses subject English (Subject Select/Dropdown) then hide Location 2 from (Locations dropdown)?
<select name="age">
<option value="8">8</div>
<option value="9">9</div>
<option value="10">10</div>
<option value="11">11</div>
</select>
<select name="subject">
<option value="eng">English</div>
<option value="maths">Maths</div>
<option value="science">Science</div>
</select>
<select name="subject">
<option value="loc-1">Location One</div>
<option value="loc-2">Location Two</div>
<option value="loc-3">Location Three</div>
</select>
Thank you!

you just need to add change function to your drop-down and according to your requirement you need to add your logic. see below example.
$(document).ready(function(){
$("#age").change(function(){
hideOption();
})
$("#subject").change(function(){
hideOption();
})
})
function hideOption(){
var age=$("#age").val();
var subject=$("#subject").val();
if(age==8 && subject=="Maths"){
$("#location [value='Location Two']").hide();
}
else{
$("#location [value='Location Two']").show();
}
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<select name="age" id='age'>
<option value="8">8</option>
<option value="9">9</option>
<option value="10">10</option>
<option value="11">11</option>
</select>
<select name="subject" id='subject'>
<option value="English">English</option>
<option value="Maths">Maths</option>
<option value="Science">Science</option>
</select>
<select name="Location" id='location'>
<option value="Location One">Location One</option>
<option value="Location Two">Location Two</option>
<option value="Location Three">Location Three</option>
</select>

You can do something like below
$(document).on('change', '.age', function(e){
var val = $(this).val();
var subject = $('.subject').find(":selected").val();
if(val == 8 && subject == 'English' ){
$('.location option[value="Two"]').hide();
} else {
$('.location option[value="Two"]').show();
}
})
$(document).on('change', '.subject', function(e){
var age = $('.age').find(":selected").val();
var val = $(this).val();
if(age == 8 && val == 'English' ){
$('.location option[value="Two"]').hide();
} else {
$('.location option[value="Two"]').show();
}
})
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<select name="age" class="age">
<option >select</8>
<option value="8">8</8>
<option value="9">9</8>
<option value="10">10</8>
<option value="11">11</8>
</select>
<select name="subject" class="subject">
<option value="English">English</8>
<option value="Maths">Maths</8>
<option value="Science">Science</8>
</select>
<select name="location" class="location">
<option value="One">Location One</8>
<option value="Two">Location Two</8>
<option value="Three">Location Three</8>
</select>

With jQuery you can use .hide() and .show() to toggle element visibility. First however, you can check if the value of a select (for example age) was changed. Based on the logic you want to have, you can for example check what the value of the change was and do something if it matches a condition.
For example:
$( "#age-select" ).change(function() {
var value = $(this).val();
if(value == 8) {
$("#location-two").hide();
} else {
$("#location-two").show();
}
});
However, notice that I added an id for the "Location Two" option ("location-two") and for the age select element. Also, to make this work properly, you have to fix the values so that they're not all 8 and fix the closing tags of the elements (not ).

How to count the number of Form selects that have had values changes in Jquery/Javascript

I have several selects in my form. If one select has had its options changed then it should increase the counter. 5 selects then counter should be 5. Essentially I want to check if all my selects have been selected so I can submit the form. I don't want to use "required".
<div id="firstPanelID"
<div class="form-group input-group">
<label class="fixingLabelAlignmentInner">Transfer Code of Center from which Infant Transferred : </label>
<div class="fixingInputAlignmentInner">
<select id="transferCodePIW" name=transferCodePIW class="form-control" style="height:32px;width:80%;">
<option disabled selected value>SELECT</option>
<option value="13240">13240 - Mowbray Maternity Hospital</option>
<option value="14994">14994 - New Somerset Hospital</option>
<option value="16011">16011 - Tygerberg Hospital</option>
<option value="8005432">8005432 - Khayelitsha District Hospital</option>
<option value="8005433">8005433 - Michell's Plain District Hospital</option>
<option value="8005435">8005435 - Red Cross Children's Hospital</option>
<option value="97777777">97777777 - Birth at Home or in Transit</option>
<option value="">Other</option>
<option value="77777777">N/A</option>
<option value="99999999">Unknown</option>
</select>
</div>
</div>
</div>
I have tried it with the following. The selects may be visible/invisible due to other radio buttons hence the visible. The function works for radio buttons but I can't get it to work for selects.
var sgroups = [];
$('#firstPanelID select:visible:selected').each(function(index, el){
var i;
for(i = 0; i < sgroups.length; i++)
if(sgroups[i] == $(el).attr('name'))
return true;
sgroups.push($(el).attr('name'));
}
);
alert(($('#firstPanelID select:visible:selected').length))

I think the code is self-explanatory.
var counter = 0;
$('select').change(function () {
var o = $(this);
if (!o.hasClass('counted')) {
counter++;
o.addClass('counted');
}
$('#counter').text(counter);
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select>
<option value="aa">aa</option>
<option value="bb">bb</option>
<option value="cc">cc</option>
</select>
<select>
<option value="2aa">2aa</option>
<option value="2bb">2bb</option>
<option value="2cc">2cc</option>
</select>
<select>
<option value="3aa">3aa</option>
<option value="3bb">3bb</option>
<option value="3cc">3cc</option>
</select>
<div id="counter">
0
</div>

If you want to check if all selects have been checked, assuming each select will have an empty value, you can do this:
function isThereAnyEmptySelection () {
let r = false;
$('select').each(function () {
if ($(this).val() === '') { // or === null, or === undefined, or === '0' etc., depending on context
r = true;
}
});
return r;
}

You can use .one() to attach a single change event to each <select> element, when count is equal to $("selector").length call .off() to remove change event, then perform action, for example, submit <form> element.
let count = 0;
$("select").one("change", function() {
++count;
console.log(count);
if (count === $("select").length) {
$("select").off("change");
// submit form here
console.log(count + " is " + $("select").length)
}
})
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select>
<option value="1">1</option>
<option value="2">2</option>
</select>
<select>
<option value="1">1</option>
<option value="2">2</option>
</select>
<select>
<option value="1">1</option>
<option value="2">2</option>
</select>
<select>
<option value="1">1</option>
<option value="2">2</option>
</select>
<select>
<option value="1">1</option>
<option value="2">2</option>
</select>

Compare select values and show alert if they match

I have 4 dropdowns from which you have to select an option.
What I am trying to do is show an alert if you chose the same option more than once. Its purpose is to keep the score for a game so a person shouldn't be able to play as 2.
At the moment the dropdown looks like this:
<select id="users_1" aria-labelledby="dropdownMenu1">
<option>Select player</option>
<?php foreach($users as $user) : ?>
<option value="<?=$user['id_user']?>"><?=$user['nume']?></option>
<?php endforeach; ?>
</select>
And what I've tried to do in JQuery is this:
$("#users_2").change(function() {
var a=$(this).val("#users_1");
var b=$(this).val("#users_2");
if(a == b) {
alert($(this).val());
}
});
And I also tried to compare them like this:
$("#users_2").change(function() {
if($(this).val() == $("#users_1").val()) {
alert($(this).val());
}
});
None seems to work and I have no clue why. I've checked and the actual values are taken from the view but the if clause cannot compare them apparently.
Thank you for any help! Much appreciated!

Get your values, don't set them
Change this…
$("#users_2").change(function() {
var a=$(this).val("#users_1");
var b=$(this).val("#users_2");
if(a == b) {
alert($(this).val());
}
});
…to this…
$("#users_2").change(function() {
var a = $("#users_1").val();
var b = $(this).val(); // equivalent to $("#users_2").val()
if(a === b) { // Use strict comparison operator as a best practice
alert(a + ' matches ' + b);
}
});
Make it dynamic
You can take it a step farther by listening to a set of elements and making your handler dynamic:
// Listen to set of all select elements.
$('select').on('change', function(e) {
// Serialize form values.
var vals = $('#select_player').serializeArray();
// Convert to simple array of just values.
vals = $.map(vals, function (val, i) {
return val.value;
});
// Remove current selection from array…
vals.splice(vals.indexOf($(this).val()), 1);
// …then check to see if it's value was already there.
if(vals.indexOf($(this).val()) !== -1) { // If value is found,
// …reset current select element to default option,
$(this).val('default');
// …and alert user with a relevant message.
alert('You cannot select this player more than once.');
};
});
label {
display: block;
margin: 10px;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form id="select_player" name="select_player">
<label>Player 1:
<select id="users_1" name="users_1">
<option value="default" selected="selected" disabled>Select player</option>
<option value="uid001">John Doe</option>
<option value="uid002">Jane Doe</option>
<option value="uid003">Jerome Smith</option>
<option value="uid004">Janet O'Public</option>
</select>
</label>
<label>Player 2:
<select id="users_2" name="users_2">
<option value="default" selected="selected" disabled>Select player</option>
<option value="uid001">John Doe</option>
<option value="uid002">Jane Doe</option>
<option value="uid003">Jerome Smith</option>
<option value="uid004">Janet O'Public</option>
</select>
</label>
<label>Player 3:
<select id="users_3" name="users_3">
<option value="default" selected="selected" disabled>Select player</option>
<option value="uid001">John Doe</option>
<option value="uid002">Jane Doe</option>
<option value="uid003">Jerome Smith</option>
<option value="uid004">Janet O'Public</option>
</select>
</label>
<label>Player 4:
<select id="users_4" name="users_4">
<option value="default" selected="selected" disabled>Select player</option>
<option value="uid001">John Doe</option>
<option value="uid002">Jane Doe</option>
<option value="uid003">Jerome Smith</option>
<option value="uid004">Janet O'Public</option>
</select>
</label>
</form>

I used the same class on all the dropdowns and then use only one event handler.
$('.dropdown').on('change', function (event) {
var selectedValue = $(event.currentTarget).val();
var matchedDropdowns = $('.dropdown').filter(function (index) {
return $(this).val() === selectedValue;
});
if (matchedDropdowns.length > 1) {
alert("Alert Alert!")
}
})
In the event handlers I can get the selected value, filter all the dropdowns that match that value and if I get more than 1 dropdown I will just show the alert.
You can check it on fiddle.

Remove option in select

<select class="one">
<option></option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<br />
<select class="one">
<option></option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<br />
<select class="one">
<option></option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
$(".one").change(function(){
})
I would like make - for example if i select in first position option 1 then i others selects this option should be removed.
So if i in first select i select 1 then in select second and third i have only option 2 and 3. If in second select i select 2 then in last select i have only option 3.
How can i make it? I would like use jQuery.
LIVE: http://jsfiddle.net/9N9Tz/1/

If you need to sort something, consider using something like jQuery UI sortable as a bunch of drop down menus make a really poor UX for that.
But to answer your question:
var $selects = $('.one');
$selects.on("keyup click change", function(e) {
$selects.not(this).trigger('updateselection');
}).on("updateselection", function(e, data) {
var $this = $(this);
$this.children().show();
$selects.not(this).each(function() {
var value = $(this).val();
if (value) {
$this.children('[value="' + value + '"]').hide();
}
});
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select class="one">
<option></option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<br />
<select class="one">
<option></option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<br />
<select class="one">
<option></option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
Hiding an option works in current firefox. I'm not sure about legacy browser. Hiding, but not removing, the element makes sure that you can change your selection without having crippled your input elements.

Here you go http://jsfiddle.net/Calou/9N9Tz/6/.
When the value of the <select>s changes, just take this value and search for the <option>s with this value in the others <select>s and remove them.
$(".one").change(function(){
var val = this.value
if (val !== '') {
$(this).siblings().find('option[value=' + val + ']').remove()
}
})

// As soon as all selects have one class, you'll have to distinguish them:
$(".one").each(function() {
// Now this corresponds to one select (in the loop over all)
$(this).change(function() {
// Fix what've done before
$('option').show();
// Find every other select, find an option in it
// that has the same value that is selected in current select
// (sorry for the description)
$('.one').not(this).find('option[value=' + $(this).find('option:selected').val() +']').hide();
});
})​;​
jsFiddle

It will be easy if you use different class for second and third select element
$(".one").change(function(){
var val = parseInt($(this).val());
$('.two,.three').find('option:contains('+val+')').remove();
});
EDIT:
Updated code to apply for multiple selects. [Thanks to all commentators and Alex for bringing it to notice ]
$(".one").change(function(){
var val = parseInt($(this).val());
$(this).siblings().find('option:contains('+val+')').remove();
});