We Keep Coding

Replacing options on <select> dynamically from JavaScript array

In a bespoke shopping cart, I pull from my database a list of options that a particular product has. The number of these options can vary by product.
I then turn that list of options into a JavaScript array.
An example with 3 options:
{"Small":{"Super":{"Pack":"parta","Case":"parte"},"Maxi":{"Pack":"partb","Case":"partf"}},"Large":{"Super":{"Pack":"partc","Case":"partg"}},"X Large":{"Maxi":{"Pack":"partd"}}}
Using the above, I would now like to generate an HTML select field, listing all the "first" options:
<select>
<option value="Small">Small</option>
<option value="Large">Large</option>
<option value="X Large">X Large</option>
</select>
Once the user has selected the first option, I then need another <select> box to then load with options that are available for their selection. So, if they selected "Small" from above, the new select box would be:
<select>
<option value="Super">Super</option>
<option value="Maxi">Maxi</option>
</select>
Finally, when they select from this list, a 3rd select box loads in the final options, along with the part numbers as values:
<select>
<option value="parta">Pack</option>
<option value="parte">Case</option>
</select>
The number of options can vary, from zero to 4. But, each time when options are available, I need to pull the part number based on the users selection. The part number doesn't necessarily need to be the value of the last select, it can be pushed to a new hidden variable.
I can achieve this using ajax, by making an ajax call every time a selection is chosen, but can it be done via JavaScript / jQuery, without having to make ajax calls, given that the array is on the page and available to use?

When you dynamically create the select element, also determine which "node" in your tree structure goes with that element, and use it to:
add a default "Please select..." option to the select element
populate the select element further with the real options
determine the deeper node when an option is selected (also when the initial selection is made when the element is created), and use it to create the next select element with the same function
This cascade stops when the deeper node does not exist (when "Please select..." is selected) or it happens to be a string and not an object.
Here is some code for inspiration:
let optionTree = {"Small":{"Super":{"Pack":"parta","Case":"parte"},"Maxi":{"Pack":"partb","Case":"partf"}},"Large":{"Super":{"Pack":"partc","Case":"partg"}},"X Large":{"Maxi":{"Pack":"partd"}}};
let container = document.querySelector("#container");
addSelector(optionTree);
function addSelector(node) {
let select = document.createElement("select");
// Start with the default option:
let option = document.createElement("option");
option.text = "Please select...";
select.add(option);
for (let key in node) { // Populate the select element
let option = document.createElement("option");
option.value = key;
option.text = key;
select.add(option);
}
container.appendChild(select); // Add it to the page
function change() {
// Remove select elements that come after the selection
while (select.nextElementSibling) {
select.nextElementSibling.remove();
}
let key = select.value;
if (node[key] && typeof node[key] !== "string") {
addSelector(node[key]); // Create the next select element(s)
}
}
// Call the above function whenever a selection is made
select.addEventListener("change", change);
change(); // ... and also call it now
}
<div id="container"></div>

Assuming you already have the three select elements in the DOM, you can populate the first select, and add a change event listener to both the first and second to achieve this. Try this
let $s1 = document.querySelector('#select-1');
let $s2 = document.querySelector('#select-2');
let $s3 = document.querySelector('#select-3');
let object = {"Small":{"Super":{"Pack":"parta","Case":"parte"},"Maxi":{"Pack":"partb","Case":"partf"}},"Large":{"Super":{"Pack":"partc","Case":"partg"}},"X Large":{"Maxi":{"Pack":"partd"}}};
// add options to first select
$s1.innerHTML = '<option></option>'; // empty select
Object.keys(object).forEach(val => $s1.append(new Option(val, val))); // append children
$s1.dispatchEvent(new Event('change')); // trigger change event
// listen to change event on first select/get options for second select
$s1.addEventListener('change', function(e){
$s2.innerHTML = '<option></option>'; // empty select
// append children
Object.keys(object[e.target.value] ?? []).forEach(val => {
$s2.appendChild(new Option(val, val));
});
// trigger change event
$s2.dispatchEvent(new Event('change'));
});
// listen to change event on second select/get options for third select
$s2.addEventListener('change', function(e){
$s3.innerHTML = '<option></option>'; // empty select
// append children
Object.entries(object[$s1.value]?.[e.target.value] ?? []).forEach(([key, val]) => {
$s3.appendChild(new Option(key, val));
});
});
select {min-width:80px}
<select id="select-1"></select>
<select id="select-2"></select>
<select id="select-3"></select>

javascript hide/show items in dropdown list

I started studying javascripting and was wondering if anyone know how to hide values in dropdown list for html?
For example: a dropdwon list with values
Select One
Item1
Item2
Item3
Item4
Item5
I wanna hide the Item 4 and 5, like this and show it when "Show... " is clicked.
Select One
Item1
Item2
Item3
Show 2 more items (Item 4 and 5 hidden)
Is that possible? Below is a piece of code i already started.
var css = select;
var markers = cluster.getMarkers();
var markersLength = markers.length;
var nextOption = new Option("Select One");
css.add(nextOption, 0);
for(var i = 0; i < markersLength; i++) {
nextOption = new Option(markers[i].title);
try {
css.add(nextOption, -1);
} catch (e) {
css.add(nextOption, null);
}
}

You want a generic solution, so tag the more option and the hidden items with classes.
It turns out you cannot consistently style-out options in a select across browsers, so you need to dynamically alter the list options: Refer to this question: How to hide a <option> in a <select> menu with CSS?
Final solution (append elements from another hidden select):
JSFiddle: http://jsfiddle.net/TrueBlueAussie/93D3h/12/
HTML:
Select One
<select class="hidden">
<option>Item4</option>
<option>Item5</option>
<option>Item6</option>
<option>Item7</option>
<select>
<select>
<option>Item1</option>
<option>Item2</option>
<option>Item3</option>
<option class="more">More</option>
</select>
jQuery:
$('select').change(function(){
var $select = $(this);
if ($select.val() == "More"){
$('.more').remove();
$select.append($('.hidden').children());
}
});
Previous info:
Then on then select change event you hide the more option and show the hidden elements:
JSFiddle: http://jsfiddle.net/TrueBlueAussie/93D3h/2/
$('select').change(function(){
var $select = $(this);
if ($select.val() == "More"){
$('.more').hide().prevAll('.hidden').show();
}
});
There appears to be a weird bug in selects as the last item is always visible (even when styled out!). I added a blank entry to fix this for now. This is also why I did not place the hidden items after the more as the last one always shows (what a strange bug - have asked that as a new question: Why is last select option always shown, even when styled out).
You will also want to clear the selected value of "More" as that will no longer exist.
e.g. http://jsfiddle.net/TrueBlueAussie/93D3h/3/
$('select').change(function () {
var $select = $(this);
if ($select.val() == "More") {
$('.more').hide().prevAll('.hidden').show();
$select.val('');
}
});
Followup:
Based on my related question, I was pointed to this one: How to hide a <option> in a <select> menu with CSS? Apparently you cannot style out select options consistently, so adding the items to the list dynamically would be the ideal solution.

Here's my solution:
Html
<select id="test">
<option value="1">Select One</option>
<option value="2">Item 1</option>
<option value="3">Item 2</option>
<option value="4">Item 3</option>
<option value="5">Select Two</option>
<option value="6">Item 4</option>
<option value="7">Item 5</option>
</select>
Script
var array1 = ["1","6","7"];
var array2 = ["1","2","3","4"];
var arrayAll = ["1","2","3","4","5","6","7"];
function hideOptions(array) {
for (var i = 0; i < array.length; i++) {
$('#test option[value="' + array[i] + '"]').hide();
}
}
function showOptions(array) {
for (var i = 0; i < array.length; i++) {
$('#test option[value="' + array[i] + '"]').show();
}
}
$("#test").change(function(){
if($("#test").val()=="5"){
hideOptions(array2);
showOptions(array1);
}
if($("#test").val()=="1"){
hideOptions(array1);
showOptions(array2);
}
});
hideOptions(array1);
here's the fiddle

What about something like:
<head>
<script type="text/javascript">
function makeDynamicOption(target, threshold, messageMore, messageLess) {
var allOptions = collectOptions();
target.addEventListener("change", updateOptions, false); // Use your own event manager
showOptions(threshold);
addMessage(messageMore);
// ---
function collectOptions() {
var options = [];
for(var ii=0; ii<target.options.length; ii++) {
options.push(target.options[ii]);
}
return options;
}
function updateOptions() {
var selectedText = this.options[this.selectedIndex].text;
if (selectedText == messageMore) {
showOptions(allOptions.length);
addMessage(messageLess);
} else if (selectedText == messageLess) {
showOptions(threshold);
addMessage(messageMore);
}
}
function showOptions(upToIndex) {
removeOptions();
for (var ii=0; ii<upToIndex; ii++) {
target.options[ii] = allOptions[ii];
}
}
function removeOptions() {
while(target.options.length > 0) {
target.removeChild(target.options[0]);
}
}
function addMessage(message) {
target.options[target.options.length] = new Option(message, "");
}
}
</script>
</head>
<body>
<select id="foo">
<option value="value1">item1</option>
<option value="value2">item2</option>
<option value="value3">item3</option>
<option value="value4">item4</option>
<option value="value5">item5</option>
</select>
<script type="text/javascript">
makeDynamicOption(
document.getElementById("foo"),
3,
"More...",
"Less..."
);
</script>
</body>
This design separates the lib part (to be linked in the HEAD as an external script) from the activation part. It also lets you inject localized text while generating the view, and preserve existing options in case you have other scripts interacting with them. Note that you should still use your own event manager, and not addEventListener directly as shown in the script, for better cross-browser support.
EDIT: here's how the scripts works:
You call the makeDynamicOptions() function on the select object you want to augment, passing the number of options you want to display, as well as messages to expand/collapse other options. The messages can be written by the view manager, i.e. it could be easily localized if needed.
The first initialization step sees that all original options be collected, so that they can be added back when the user wants to expand the select. Note that we collect the objects themselves, and not only their value/text property values, as other scripts could reference these objects.
The second initialization step registers a change handler on the select, so as to trigger the update on the options list. The script uses addEventListener, but one should substitute one's own event management mechanism, for better cross-browser support.
The last initialization step collapses the select in the intended start position.
The rest is pretty straightforward. Once the user selects an option, the script decides whether the list of options should be repopulated, by analyzing the text of the selected option, and comparing it to the provided expand/collapse labels. If options are to be redrawn, then the script removes all options, adds the expected ones, then adds the new expand/collapse message.
HTH.

Alert when user select the same <option> in dynamically created <selects>

I have a PHP page that creates multiple selects depending on how many the page before it gives it and creates the same number of options that there are selected (it's to choose the priority).
<select name="select1" id="idSelect" onchange="javascript:SelectOnChange();">
<option value="Select one">Select one</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
What I want to do is, whenever the user chooses an option that was already selected in another selection, to show an alert in order to let them know that their choice has already been taken and deny the change.
I want to compare the currently selected option to every previously selected option every time the user selects something from every select.

Basically your looking for a change event to loop through each select and notify duplicates.
$("select").change(function() {
var currentSelection = this.value;
$("select").each(function() {
if (this.value == currentSelection) {
alert("you've already chosen this!");
}
});
});
Something like this should work

Listen for change events
Get the element's seletedIndex
Grab all of the selects with getElementsByTagName()
Loop through and get the selected index
Compare to see if used

This could maybe work :
var $selects = $('select');
// WHen a select is changed.
$selects.onchange(function() {
// Storing it's selected value, assuming there is only one per select.
var value = $(this).selected().first().attr('value');
var $changedSelect = $(this);
// For each select...
$selects.each(function() {
var $otherSelect = $(this);
// ...that is not the one that just changed.
if( ! $otherSelect.is($changedSelect)) {
// If that other select's selected value is the same as the changed one's
if($otherSelect.selected().first().attr('value') === value) {
alert('...');
}
}
});
}
I didn't try it though, you might have to change a few details in it if it doesn't work.

how to find all the select elements that have changed?

let's say I have a form that contains several "select" element that the User can choose.
when ready to submit, I need to find all the "select" that have changed.
how can I do it?
for example:
<form>
<input type="text" name="a"/>
<select name="b">...</select>
<select name="c">...</select>
<select name="d">...</select>
</form>

Using jQuery, something like this should work:
$('select').change(function() {
$(this).addClass('changed');
});
$('form').submit(function() {
var changed_selects = $('select.changed');
// do what you want with the changed selects
});

I would take advantage of the defaultSelected property on HTMLOptionElement instead of trying to keep track of selects that have changed:
form.onsubmit = function() {
var selects = form.getElementsByTagName("select")
, i
, changedSelects = []
, selected
, select;
/* Iterate over all selects in the form: */
for (i = 0; i < selects.length; i++) {
select = selects[i];
/* Get the currently selected <option> element: */
selected = select[select.selectedIndex];
/* Determine if the currently selected option is the one selected by default: */
if (!selected.defaultSelected) {
changedSelects.push(select);
}
}
alert(changedSelects.length);
}
You can iterate over all of the select elements on your form, determine if the selected option is the one that was selected by default, and push each one whose selected option wasn't the default into an array.
Example: http://jsfiddle.net/andrewwhitaker/abFr3/

You could register an event listener (using onchange, etc.) to determine if any changes were made.
Alternatively, you could keep a private copy of all of the previous values, then run a comparison before submit to check for changes.

Do something like:
var selectedVal = $("select[name='a'] option:selected").val();
//check this with your default selected val

You can attach the onchange event listener to each <select> element. When the event is triggered, you can store the actual elements in an a temporary array and reference it later when you are ready to submit. Note that the array can hold the actual DOM elements.

You need to clarify what you mean by "the select have changed".
If you mean have changed from their default value, then you should have one option on each select (usually the first) set as the default selected option. Then you can iterate over the selects and see if the option with the selected attribute (or where the defaultSelected property is true) is the selected option, e.g.
<script>
function anyChanged(){
var select, selects = document.getElementsByTagName('select');
for (var i=0, iLen=selects.length; i<iLen; i++) {
select = selects[i];
if (!select.options[select.selectedIndex].defaultSelected) {
// the selected option isn't the default
alert('select ' + (select.id || select.name) + ' changed');
}
}
}
</script>
<select name="one">
<option selected>one
<option>two
<option>three
</select>
<button onclick="anyChanged()">Check</button>
However, if you want to see if the user has changed the selected option based on some other logic, you need to say what it is.

Problem with multiple select removing more than 1 option

There seems to be a problem with the JS Code for Opera browsers, as it only removes the last option tag that is selected within a multiple select tag, can someone please help me.
Here is the HTML for this:
<select id="actions_list" name="layouts" multiple style="height: 128px; width: 300px;">
<option value="forum">forum</option>
<option value="collapse">collapse</option>
<option value="[topic]">[topic]</option>
<option value="[board]">[board]</option>
</select>
Of course it's within a form tag, but there's a ton more code involved with this form, but here is the relevant info for this.
Here is the JS that should handle this, but only removes the last selected option in Opera, not sure about other browsers, but it really needs to remove all selected options, not just the last selected option...
var action_list = document.getElementById("actions_list");
var i = action_list.options.length;
while(i--)
{
if (action_list.options[i].selected)
{
action_list.remove(i);
}
}
What is wrong with this? I can't figure it out one bit.

It's easiest to do this with jQuery but it you want to do this using plain Javascript you can.
The problem you are experiencing is that when you remove an item from the options list in Opera it deselects all the selected items, so only the first is removed. A workaround is to first remember which items were selected before removing any.
var action_list = document.getElementById("actions_list");
// Remember selected items.
var is_selected = [];
for (var i = 0; i < action_list.options.length; ++i)
{
is_selected[i] = action_list.options[i].selected;
}
// Remove selected items.
i = action_list.options.length;
while (i--)
{
if (is_selected[i])
{
action_list.remove(i);
}
}

You can do it much easier using jQuery:
$('#actions_list option:selected').remove()

$.each($('[name="alltags"] option:selected'), function( index, value ) {
$(this).remove();
});
try this instead to remove multiple selection

Removing multiple options from select based on condition:
while(SelectBox.length > 1){
if(SelectBox[SelectBox.length -1].text != "YourCondition"){
SelectBox.remove(SelectBox.length -1);
}
}