for example - a profile page - users want to change some values in select tags
you cannot say - <select id='lorem' value='ipsum'>
you must go to javascript - $('#lorem').val('ipsum')
is this really true ?
is there any better practice - if you have a lot of select tags ?
btw - why html developers made this like this - there must be some strong reason
Your "question" really embodies multiple questions, hence I divided my answer into multiple sections.
<select> and <option>
To select an <option> of <select> initially, add the selected-attribute to <option>. Selecting an <option> makes the <select> have the value of the selected option.
var select = document.querySelector('select');
var code = document.querySelector('code');
select.addEventListener('change', () => code.textContent = select.value);
code.textContent = select.value;
body {display:flex;align-items:center;gap:0.5rem}
code {padding:0 0.2rem;background:lightgray}
<select>
<option value="first">First option</option>
<option value="second" selected>Second option, initially selected</option>
<option value="third">Third option</option>
</select>
<span>Select's 'value': <code></code></span>
Giving <select> a value-attribute will be ignored by the browser-engine, since HTML5 doesn't specify the <select>-tag to have a value-attribute.
Note: The HTML-attribute value and the JavaScript property .value are not necessarily related to each other.
See this example for reference:
var select = document.querySelector('select');
var code = document.querySelector('span > code');
select.addEventListener('change', evt => {
code.textContent = evt.target.value;
});
code.textContent = select.value;
body {display:flex;flex-flow:column;align-items:flex-start;gap:0.5rem}
code {padding:0 0.1rem;background:lightgray}
<div>
<code><select></code> has the attribute <code>value="from-select"</code>.
</div>
<select value="from-select">
<option value="from-opt1">Opt1</option>
<option value="from-opt2">Opt2</option>
</select>
<span>Select's 'value': <code></code></span>
To change the value of an <option> dynamically, you would have to use JavaScript.
var input = document.querySelector('input');
var option = document.querySelector('option');
var code = document.querySelector('code');
// Ignore; update 'pre.textContent' when changing 'value'
option.setAttribute = function(name, value) {
HTMLElement.prototype.setAttribute.call(this, name, value);
if (name === 'value') code.textContent = value;
};
// How to change the 'value'-attribute using JS
document.querySelector('button').addEventListener('click', () => {
option.setAttribute('value', input.value);
input.value = '';
});
body {display:flex;flex-flow:column;align-items:flex-start;gap:0.5rem}
code {padding:0.1rem 0.2rem;background:lightgray}
<span>
<input>
<button>Change value of 'Option'</button>
</span>
<select>
<option value="initial-value">Option</option>
</select>
<span>Option's value: <code>initial-value</code></span>
Regarding "why html developers made this like this"
Paraphrased: Why can't HTML change its markup on its own?
Reason is, HTML was initially created for scientific documents served via the internet.
Since the internet is by nature a web of interconnected, potentially completely different devices, HTML had to be as unspecific and "device-agnostic" as possible, to allow rendering it on virtually any device that has a display.
For that reason, any further resource (e.g. stylesheets, scripts, images) should only be optional for the rendering of the HTML, as the HTML should be renderable "as is".
HTML should also be backwards-compatible, meaning that future changes to the HTML specification should in no way hinder the serving of the HTML. That means, any unknown... thing, basically, will be ignored by the rendering engine (todays browsers) so that all the then-existing features can still work as intended.
Initially, HTML was not intended to have any further functionality than serving static content. However, over the last few decades, the internet has had its "boom" of technological advancement, and now, JavaScript is de facto part of any browser-engine and website, enabling them to have advanced functionality and be interactive.
The internet is in a state of ongoing development, and always will be. Neglecting the new state of the internet and its specification (e.g. for the browser-engines, etc.) would mean that one is not moving with the times, withholding new, modern and current information and knowledge from oneself, essentially leaving one behind.
"Tradition" is difficult to find in any technical field, as new advancements and discoveries are simply spoken part of them.
To learn more about the roots of the internet (even though the video is thematically about CSS) I recommend watching MDN's video about why CSS is weird (and how HTML came to be).
Regarding your "question" ...
as you have further explained in the comments:
I have some data about each user in database. Those data are from
registration form. That form has select tags. Now, user want to change
some data on his profile. Tha data need to be presented on select
tags. It would be normal to do that using value attribute, like in any
other input - without javascript
You could do it two ways:
Create a <form> with one field for each user-data. With this, you have two more options:
Prepare the fields to hold their current data. The user can then submit his changes easily.
Leave the fields empty. If a field is empty after submission, ignore the proposed "change".
Let the user select what data to change one at a time. Again, two more options to achieve this:
Fetch the current data for that field. The user can change it and then submit it easily, again.
Let the user enter the new data anew, then submit it.
Here is a simple example of how the HTML for option 2.2 could look when implemented:
Note: I changed the <button>'s default type from type="submit" to type="button" for demonstration-purposes.
var select = document.querySelector('select');
var input = document.querySelector('input');
document.querySelector('button').addEventListener('click', () => {
console.log(`Would change user-data '${select.value}' to the value '${input.value}'.`);
});
<form>
<select>
<option value="name">Name</option>
<option value="address">Address</option>
<option value="email">E-Mail</option>
</select>
<input>
<button type="button">Submit</button>
</form>
I have an input form that lets me select from multiple options, and do something when the user changes the selection. Eg,
<select onChange="javascript:doSomething();">
<option>A</option>
<option>B</option>
<option>C</option>
</select>
Now, doSomething() only gets triggered when the selection changes.
I want to trigger doSomething() when the user selects any option, possibly the same one again.
I have tried using an "onClick" handler, but that gets triggered before the user starts the selection process.
So, is there a way to trigger a function on every select by the user?
Update:
The answer suggested by Darryl seemed to work, but it doesn't work consistently. Sometimes the event gets triggered as soon as user clicks the drop-down menu, even before the user has finished the selection process!
I needed something exactly the same. This is what worked for me:
<select onchange="doSomething();" onfocus="this.selectedIndex = -1;">
<option>A</option>
<option>B</option>
<option>C</option>
</select>
Supports this:
when the user selects any option, possibly the same one again
Here is the simplest way:
<select name="ab" onchange="if (this.selectedIndex) doSomething();">
<option value="-1">--</option>
<option value="1">option 1</option>
<option value="2">option 2</option>
<option value="3">option 3</option>
</select>
Works both with mouse selection and keyboard Up/Down keys whes select is focused.
I had the same problem when I was creating a design a few months back. The solution I found was to use .live("change", function()) in combination with .blur() on the element you are using.
If you wish to have it do something when the user simply clicks, instead of changing, just replace change with click.
I assigned my dropdown an ID, selected, and used the following:
$(function () {
$("#selected").live("change", function () {
// do whatever you need to do
// you want the element to lose focus immediately
// this is key to get this working.
$('#selected').blur();
});
});
I saw this one didn't have a selected answer, so I figured I'd give my input. This worked excellently for me, so hopefully someone else can use this code when they get stuck.
http://api.jquery.com/live/
Edit: Use the on selector as opposed to .live. See jQuery .on()
Just an idea, but is it possible to put an onclick on each of the <option> elements?
<select>
<option onclick="doSomething(this);">A</option>
<option onclick="doSomething(this);">B</option>
<option onclick="doSomething(this);">C</option>
</select>
Another option could be to use onblur on the select. This will fire anytime the user clicks away from the select. At this point you could determine what option was selected. To have this even trigger at the correct time, the onclick of the option's could blur the field (make something else active or just .blur() in jQuery).
If you really need this to work like this, I would do this (to ensure it works by keyboard and mouse)
Add an onfocus event handler to the select to set the "current" value
Add an onclick event handler to the select to handle mouse changes
Add an onkeypress event handler to the select to handle keyboard changes
Unfortunately the onclick will run multiple times (e.g. on onpening the select... and on selection/close) and the onkeypress may fire when nothing changes...
<script>
function setInitial(obj){
obj._initValue = obj.value;
}
function doSomething(obj){
//if you want to verify a change took place...
if(obj._initValue == obj.value){
//do nothing, no actual change occurred...
//or in your case if you want to make a minor update
doMinorUpdate();
} else {
//change happened
getNewData(obj.value);
}
}
</script>
<select onfocus="setInitial(this);" onclick="doSomething();" onkeypress="doSomething();">
...
</select>
The onclick approach is not entirely bad but as said, it will not be triggered when the value isn't changed by a mouse-click.
It is however possible to trigger the onclick event in the onchange event.
<select onchange="{doSomething(...);if(this.options[this.selectedIndex].onclick != null){this.options[this.selectedIndex].onclick(this);}}">
<option onclick="doSomethingElse(...);" value="A">A</option>
<option onclick="doSomethingElse(..);" value="B">B</option>
<option onclick="doSomethingElse(..);" value="Foo">C</option>
</select>
I know this question is very old now, but for anyone still running into this problem, I have achieved this with my own website by adding an onInput event to my option tag, then in that called function, retrieving the value of that option input.
<select id='dropdown' onInput='myFunction()'>
<option value='1'>1</option>
<option value='2'>2</option>
</select>
<p>Output: </p>
<span id='output'></span>
<script type='text/javascript'>
function myFunction() {
var optionValue = document.getElementById("dropdown").value;
document.getElementById("output").innerHTML = optionValue;
}
</script>
Going to expand on jitbit's answer. I found it weird when you clicked the drop down and then clicked off the drop down without selecting anything. Ended up with something along the lines of:
var lastSelectedOption = null;
DDChange = function(Dd) {
//Blur after change so that clicking again without
//losing focus re-triggers onfocus.
Dd.blur();
//The rest is whatever you want in the change.
var tcs = $("span.on_change_times");
tcs.html(+tcs.html() + 1);
$("span.selected_index").html(Dd.prop("selectedIndex"));
return false;
};
DDFocus = function(Dd) {
lastSelectedOption = Dd.prop("selectedIndex");
Dd.prop("selectedIndex", -1);
$("span.selected_index").html(Dd.prop("selectedIndex"));
return false;
};
//On blur, set it back to the value before they clicked
//away without selecting an option.
//
//This is what is typically weird for the user since they
//might click on the dropdown to look at other options,
//realize they didn't what to change anything, and
//click off the dropdown.
DDBlur = function(Dd) {
if (Dd.prop("selectedIndex") === -1)
Dd.prop("selectedIndex", lastSelectedOption);
$("span.selected_index").html(Dd.prop("selectedIndex"));
return false;
};
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<select id="Dd" onchange="DDChange($(this));" onfocus="DDFocus($(this));" onblur="DDBlur($(this));">
<option>1</option>
<option>2</option>
</select>
<br/>
<br/>Selected index: <span class="selected_index"></span>
<br/>Times onchange triggered: <span class="on_change_times">0</span>
This makes a little more sense for the user and allows JavaScript to run every time they select any option including an earlier option.
The downside to this approach is that it breaks the ability to tab onto a drop down and use the arrow keys to select the value. This was acceptable for me since all the users click everything all the time until the end of eternity.
To properly fire an event every time the user selects something(even the same option), you just need to trick the select box.
Like others have said, specify a negative selectedIndex on focus to force the change event. While this does allow you to trick the select box, it won't work after that as long as it still has focus. The simple fix is to force the select box to blur, shown below.
Standard JS/HTML:
<select onchange="myCallback();" onfocus="this.selectedIndex=-1;this.blur();">
<option>A</option>
<option>B</option>
<option>C</option>
</select>
jQuery Plugin:
<select>
<option>A</option>
<option>B</option>
<option>C</option>
</select>
<script type="text/javascript">
$.fn.alwaysChange = function(callback) {
return this.each(function(){
var elem = this;
var $this = $(this);
$this.change(function(){
if(callback) callback($this.val());
}).focus(function(){
elem.selectedIndex = -1;
elem.blur();
});
});
}
$('select').alwaysChange(function(val){
// Optional change event callback,
// shorthand for $('select').alwaysChange().change(function(){});
});
</script>
You can see a working demo here.
first of all u use onChange as an event handler and then use flag variable to make it do the function u want every time u make a change
<select
var list = document.getElementById("list");
var flag = true ;
list.onchange = function () {
if(flag){
document.bgColor ="red";
flag = false;
}else{
document.bgColor ="green";
flag = true;
}
}
<select id="list">
<option>op1</option>
<option>op2</option>
<option>op3</option>
</select>
This may not directly answer your question, but this problem could be solved by simple design level adjustments. I understand this may not be 100% applicable to all use-cases, but I strongly urge you to consider re-thinking your user flow of your application and if the following design suggestion can be implemented.
I decided to do something simple than hacking alternatives for onChange() using other events that were not really meant for this purpose (blur, click, etc.)
The way I solved it:
Simply pre-pend a placeholder option tag such as select that has no value to it.
So, instead of just using the following structure, which requires hack-y alternatives:
<select>
<option>A</option>
<option>B</option>
<option>C</option>
</select>
Consider using this:
<select>
<option selected="selected">Select...</option>
<option>A</option>
<option>B</option>
<option>C</option>
</select>
So, this way, your code is a LOT more simplified and the onChange will work as expected, every time the user decides to select something other than the default value. You could even add the disabled attribute to the first option if you don't want them to select it again and force them to select something from the options, thus triggering an onChange() fire.
At the time of this answer, I'm writing a complex Vue application and I found that this design choice has simplified my code a lot. I spent hours on this problem before I settled down with this solution and I didn't have to re-write a lot of my code. However, if I went with the hacky alternatives, I would have needed to account for the edge cases, to prevent double firing of ajax requests, etc. This also doesn't mess up the default browser behaviour as a nice bonus (tested on mobile browsers as well).
Sometimes, you just need to take a step back and think about the big picture for the simplest solution.
Add an extra option as the first, like the header of a column, which will be the default value of the dropdown button before click it and reset at the end of doSomething(), so when choose A/B/C, the onchange event always trigs, when the selection is State, do nothing and return. onclick is very unstable as many people mentioned before. So all we need to do is to make an initial button label which is different as your true options so the onchange will work on any option.
<select id="btnState" onchange="doSomething(this)">
<option value="State" selected="selected">State</option>
<option value="A">A</option>
<option value="B">B</option>
<option value="C">C</option>
</select>
function doSomething(obj)
{
var btnValue = obj.options[obj.selectedIndex].value;
if (btnValue == "State")
{
//do nothing
return;
}
// Do your thing here
// reset
obj.selectedIndex = 0;
}
Actually, the onclick events will NOT fire when the user uses the keyboard to change the selection in the select control. You might have to use a combination of onChange and onClick to get the behavior you're looking for.
The wonderful thing about the select tag (in this scenario) is that it will grab its value from the option tags.
Try:
<select onChange="javascript:doSomething(this.value);">
<option value="A">A</option>
<option value="B">B</option>
<option value="Foo">C</option>
</select>
Worked decent for me.
What I did when faced with a similar Problem is I added an 'onFocus' to the select box which appends a new generic option ('select an option'or something similar) and default it as the selected option.
So my goal was to be able to select the same value multiple times which essentially overwrites the the onchange() function and turn it into a useful onclick() method.
Based on the suggestions above I came up with this which works for me.
<select name="ab" id="hi" onchange="if (typeof(this.selectedIndex) != undefined) {alert($('#hi').val()); this.blur();}" onfocus="this.selectedIndex = -1;">
<option value="-1">--</option>
<option value="1">option 1</option>
<option value="2">option 2</option>
<option value="3">option 3</option>
</select>
http://jsfiddle.net/dR9tH/19/
2022 VANILLA JAVASCRIPT
...because this is a top hit on Google.
Original Poster did NOT ask for a JQuery solution, yet all answers ONLY demonstrate JQuery or inline SELECT tag event.
Use an event listener with the 'change' event.
const selectDropdown = document.querySelector('select');
selectDropdown.addEventListener('change', function (e) { /* your code */ });
... or call a seperate function:
function yourFunc(e) { /* your code here */ }
const selectDropdown = document.querySelector('select');
selectDropdown.addEventListener('change', yourFunc);
Kindly note that Event Handlers are not supported for the OPTION tag on IE, with a quick thinking..I came up with this solution, try it and give me your feedback:
<script>
var flag = true;
function resetIndex(selObj) {
if(flag) selObj.selectedIndex = -1;
flag = true;
}
function doSomething(selObj) {
alert(selObj.value)
flag = false;
}
</script>
<select onchange="doSomething(this)" onclick="resetIndex(this)">
<option value="A">A</option>
<option value="B">B</option>
<option value="C">C</option>
</select>
What I'm doing here actually is resetting the select index so that the onchange event will be triggered always, true that you we lose the selected item when you click and it maybe annoying if your list is long, but it may help you in someway..
use jquery:
<select class="target">
<option>A</option>
<option>B</option>
<option>C</option>
</select>
<script>
$('.target').change(function() { doSomething(); });
</script>
Here's my solution, completely different to any else on here. It uses the mouse position to figure out if an option was clicked as oppose to clicking on the select box to open the dropdown. It makes use of the event.screenY position as this is the only reliable cross browser variable. A hover event has to be attached first so it can figure out the controls position relative to the screen before the click event.
var select = $("select");
var screenDif = 0;
select.bind("hover", function (e) {
screenDif = e.screenY - e.clientY;
});
select.bind("click", function (e) {
var element = $(e.target);
var eventHorizon = screenDif + element.offset().top + element.height() - $(window).scrollTop();
if (e.screenY > eventHorizon)
alert("option clicked");
});
Here is my jsFiddle
http://jsfiddle.net/sU7EV/4/
you should try using option:selected
$("select option:selected").click(doSomething);
What works for me:
<select id='myID' onchange='doSomething();'>
<option value='0' selected> Select Option </option>
<option value='1' onclick='if (!document.getElementById("myID").onchange()) doSomething();' > A </option>
<option value='2' onclick='if (!document.getElementById("myID").onchange()) doSomething();' > B </option>
</select>
In that way, onchange calls 'doSomething()' when the option changes, and
onclick calls 'doSomething()' when onchange event is false, in other words, when you select the same option
Try this (event triggered exactly when you select option, without option changing):
$("select").mouseup(function() {
var open = $(this).data("isopen");
if(open) {
alert('selected');
}
$(this).data("isopen", !open);
});
http://jsbin.com/dowoloka/4
The one True answer is to not use the select field (if you need to do something when you re-select same answer.)
Create a dropdown menu with conventional div, button, show/hide menu. Link: https://www.w3schools.com/howto/howto_js_dropdown.asp
Could have been avoided had one been able to add event listeners to options. If there had been an onSelect listener for select element. And if clicking on the select field didn't aggravatingly fire off mousedown, mouseup, and click all at the same time on mousedown.
<script>
function abc(selectedguy) {
alert(selectedguy);
}
</script>
<select onchange="abc(this.selectedIndex);">
<option>option one</option>
<option>option two</option>
</select>
Here you have the index returned, and in the js code you can use this return with one switch or anything you want.
Try this:
<select id="nameSelect" onfocus="javascript:document.getElementById('nameSelect').selectedIndex=-1;" onchange="doSomething(this);">
<option value="A">A</option>
<option value="B">B</option>
<option value="C">C</option>
</select>
A long while ago now but in reply to the original question, would this help ?
Just put onClick into the SELECT line.
Then put what you want each OPTION to do in the OPTION lines.
ie:
<SELECT name="your name" onClick>
<option value ="Kilometres" onClick="YourFunction()">Kilometres
-------
-------
</SELECT>
<select name="test[]"
onchange="if(this.selectedIndex < 1){this.options[this.selectedIndex].selected = !1}">
<option>1</option>
<option>2</option>
<option>3</option>
</select>
I had faced a similar need and ended up writing a angularjs directive for the same -
guthub link - angular select
Used element[0].blur(); to remove the focus off the select tag. Logic is to trigger this blur on second click of the dropdown.
as-select gets triggered even when user selects the same value in the dropdown.
DEMO - link
There are a few things you want to do here to make sure it remembers older values and triggers an onchange event even if the same option is selected again.
The first thing you want is a regular onChange event:
$("#selectbox").on("change", function(){
console.log($(this).val());
doSomething();
});
To have the onChange event trigger even when the same option is selected again, you can unset selected option when the dropdown receives focus by setting it to an invalid value. But you also want to store the previously selected value to restore it in case the user does not select any new option:
prev_select_option = ""; //some kind of global var
$("#selectbox").on("focus", function(){
prev_select_option = $(this).val(); //store currently selected value
$(this).val("unknown"); //set to an invalid value
});
The above code will allow you to trigger onchange even if the same value is selected. However, if the user clicks outside the select box, you want to restore the previous value. We do it on onBlur:
$("#selectbox").on("blur", function(){
if ($(this).val() == null) {
//because we previously set an invalid value
//and user did not select any option
$(this).val(prev_select_option);
}
});
In my application, I have a list of <select> controls. Change of selection in each of these controls can be made only after user confirmation. So I deal with it as follows:
<select onchange="changeSelect(this)" onmousedown="clickSelect(this)">
<option value="1" selected="true">A</option> // here is 'default' value 1
<option value="2" >B</option>
</select>
<select onchange="changeSelect(this)" onmousedown="clickSelect(this)">
<option value="1" >A</option>
<option value="2" selected="true">B</option> // here is 'default' value 2
</select>
// more select controls with arbitrary 'default' values, they can be added and removed dynamically
When the user clicks the select to choose another option, the clickSelect(this) method saves the currently chosen (old) selection:
function clickSelect(select) {
globalScope.previouslySelected = $(select).val();
}
And now, if the user really tries to change the selection, I ask the user for confirmation, and if she does not confirm, I use the saved value to restore the previous state:
function changeSelect(select) {
var response = confirm("Current changes to the threat log will be lost. Continue anyway?");
if (response == false) {
// change it back
$(select).val(globalScope.previouslySelected);
return;
}
}
}
Now, on IE, Chrome and Opera it works just fine. However, when I use Firefox, it does not work. THe reason is that FF calls the onmousedown handler twice during the selection -- first time when the user clicks to roll down the select control, and second time when she selects a new selection. Therefore the last remembered value of globalScope.previouslySelected will become the new selected value and not really the old one, as in other browsers.
I know using global variables is considered bad practice. This is not the issue here. Using any other storage will not make it work.
My only idea right now is to write a Firefox specific piece of code in the clickSelect(select) handler and ignore the second notification. However, for some reason the following code I found on stack overflow does not work:
if($.browser.mozilla) {
console.log("Olalala");
}
E.g., in Chrome it throws following exception:
Uncaught TypeError: Cannot read property 'mozilla' of undefined
So how can I make it work so that ti would only run in FF? Or if any of you guys have a better solution to the problem of confirmation, I would gladly hear it. Just remember, there is a dynamic set of select controls, not just a single one. It has to work for all of them. Plus they can be added or removed dynamically, so in a single page request their number can vary. User loads page with a single select control, presses a '+' button and adds another select control, etc., but the solution has to work uniformly with all the controls.
Is there a specific reason you're saving the currently selected option using the onmousedown listener? You can just initialize your global variable to hold the default option, and update it whenever a new selection is made.
Something like this:
HTML
<select id="mySelect" onchange="changeSelect(this)">
<option value="1" >A</option>
<option value="2" >B</option>
</select>
JS
var globalScope = {previouslySelected: $("#mySelect").val()};
function changeSelect(select) {
var response = confirm("Current changes to the threat log will be lost. Continue anyway?");
if (response == false) {
// change it back
$(select).val(globalScope.previouslySelected);
return;
}
globalScope.previouslySelected = $(select).val();
}
EDIT
I noticed that on Firefox, the second mousedown event's target is the option, so you can use the following code to ignore the event in this case:
$("select").mousedown(function(e) {
if ($(e.target).is('option'))
return;
globalScope.previouslySelected = $(this).val();
});
With this code you can remove the onmousedown registration from your DOM.