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Automatically changing input values when selected a new element

How can I get input values to change dynamically when I select some element from select tag. I want in this input box to be shown a proper value when I change select option.
<select onchange="changevalue()" id="selectingg">
<option value="0">...</option>
<option value="1">Comedy</option>
<option value="2">Horror</option>
<option value="3">Action</option>
<option value="4">Sci-fi</option>
<option value="5">Adventure</option>
<option value="6">Documentary</option>
<option value="7">Anime</option>
</select>
<input type = "text" id="inputting"></input>

You could use addEventListener on change event and get the value from the event.target dropdown like so:
document.getElementById("dropdownCategory").addEventListener('change', event => document.getElementById('categorySelected').value = event.target.value);
<select id="dropdownCategory">
<option value="0">...</option>
<option value="1">Comedy</option>
<option value="2">Horror</option>
<option value="3">Action</option>
</select>
<input type="text" id="categorySelected"></input>

The below code is working fine for me you may try this code.
In below code I am assigning select value to input tag value.
function changevalue(){
document.getElementById("inputting").value =
document.getElementById("selecting").value;
}
<select onchange="changevalue()" id="selecting">
<option value="0">...</option>
<option value="1">Comedy</option>
<option value="2">Horror</option>
<option value="3">Action</option>
<option value="4">Sci-fi</option>
<option value="5">Adventure</option>
<option value="6">Documentary</option>
<option value="7">Anime</option>
</select>
<input type = "text" id="inputting"></input>

Jquery change multiple select buttons with a select button

I want to change multiple select buttons's values with another select button.
Practically when someone select an option in the main select button, the other select buttons must change with that value.
EDIT: I added the code, the first is the main select button and after I select somethig there, it should change in the others.
<select class="select_format">
<option value="0.49">9x13</option>
<option value="0.59">10X15</option>
<option value="0.99">13X18</option>
<option value="1.20">15X21</option>
<option value="2.60">20X30</option>
</select>
<select name="format[]" class="format_imgs">
<option value="0.49">9x13</option>
<option value="0.59">10X15</option>
<option value="0.99">13X18</option>
<option value="1.20">15X21</option>
<option value="2.60">20X30</option>
</select>
<select name="format[]" class="format_imgs">
<option value="0.49">9x13</option>
<option value="0.59">10X15</option>
<option value="0.99">13X18</option>
<option value="1.20">15X21</option>
<option value="2.60">20X30</option>
</select>
<select name="format[]" class="format_imgs">
<option value="0.49">9x13</option>
<option value="0.59">10X15</option>
<option value="0.99">13X18</option>
<option value="1.20">15X21</option>
<option value="2.60">20X30</option>
</select>
Thanks.

Since you didn't supply code here's a guess:
$(".myTriggerButton").on("click", function() {
$(".buttonToChangeValue").each(function() {
this.value = "new value";
});
});

$('.select_format').change(function(){
$('.format_imgs').val( $(this).val() );
});
https://jsfiddle.net/7hno0ob8/1/

How can I check if Dynamically created Select Boxes have been selected

I have some code that has one contact select box hard coded and then if you click on a add button it adds more contacts. Each contact can be selected from a dropdown and give a location in at location text box.
I want on submit to be able to know if they have selected someone and if not I want to clear out the Location box as there cannot be a location if there is no contact.
<!--- The myContactCount variable is set in another part of javascript this is the current count plus one of the number of current select boxes. --->
<script type="text/javascript" language="javascript">
var e='';
var contactSelectedValue='';
for(var i=1;1<myContactCount;i++){
e = document.getElementById('myContactID_'+i);
contactSelectedValue = e.options[e.selectedIndex].value;
/* I am trying to alert the value so I can then use a if statement to check for null or even change the 'Select a Contact' value to 0 and test for that. */
alert(contactSelectedValue);
}
</script>
<!--- the ID will be 1-100 depending on how many contacts they have added --->
<select name="myContactID_#ID#">
<option value="">Select a Contact</option>
<option value="1">Abe</option>
<option value="2">Barbara</option>
<option value="3">Cavlin</option>
</select>
So after they are created dynamically they code would look like this.
<select name="myContactID_1">
<option value="">Select a Contact</option>
<option value="1">Abe</option>
<option value="2">Barbara</option>
<option value="3" selected="selected">Cavlin</option>
</select>
<select name="myContactID_2">
<option value="">Select a Contact</option>
<option value="1">Abe</option>
<option value="2" selected="selected">Barbara</option>
<option value="3">Cavlin</option>
</select>
<select name="myContactID_3">
<option value="">Select a Contact</option>
<option value="1" selected="selected">Abe</option>
<option value="2">Barbara</option>
<option value="3">Cavlin</option>
</select>

Your script has couple of issues:-
1<myContactCount instead of i<=myContactCount and you are using name in the select and
trying to fetch it by id.
Demo
Html
<select id="myContactID_1">
<option value="">Select a Contact</option>
<option value="1">Abe</option>
<option value="2">Barbara</option>
<option value="3" selected="selected">Cavlin</option>
</select>
<select id="myContactID_2">
<option value="">Select a Contact</option>
<option value="1">Abe</option>
<option value="2" selected="selected">Barbara</option>
<option value="3">Cavlin</option>
</select>
<select id="myContactID_3">
<option value="">Select a Contact</option>
<option value="1" selected="selected">Abe</option>
<option value="2">Barbara</option>
<option value="3">Cavlin</option>
</select>
JS
var e='';
var contactSelectedValue='';
for(var i=1;i<=3;i++){
e = document.getElementById('myContactID_'+i);
contactSelectedValue = e.options[e.selectedIndex].value;
/* I am trying to alert the value so I can then use a if statement to check for null or even change the 'Select a Contact' value to 0 and test for that. */
alert(contactSelectedValue);
}

Links in <select> dropdown options

Is it possible for each dropdown options to link somewhere when selected without the need for an external button?
<select>
<option value="x">x</option>
<option value="y">y</option>
</select>

You can use the onChange property. Something like:
<select onChange="window.location.href=this.value">
<option value="www.google.com">A</option>
<option value="www.aol.com">B</option>
</select>

Add an onchange event handler and set the pages location to the value
<select id="foo">
<option value="">Pick a site</option>
<option value="http://www.google.com">x</option>
<option value="http://www.yahoo.com">y</option>
</select>
<script>
document.getElementById("foo").onchange = function() {
if (this.selectedIndex!==0) {
window.location.href = this.value;
}
};
</script>

... or if you want / need to keep your option 'value' as it was, just add a new attribute:
<select id="my_selection">
<option value="x" href="/link/to/somewhere">value 1</option>
<option value="y" href="/link/to/somewhere/else">value 2</option>
</select>
<script>
document.getElementById('my_selection').onchange = function() {
window.location.href = this.children[this.selectedIndex].getAttribute('href');
}
</script>

Maybe this will help:
<select onchange="location = this.value;">
<option value="home.html">Home</option>
<option value="contact.html">Contact</option>
<option value="about.html">About</option>
</select>

This is an old question, I know but for 2019 peeps:
Like above if you just want to change the URL you can do this:
<select onChange="window.location.href=this.value">
<option value="www.google.com">A</option>
<option value="www.aol.com">B</option>
</select>
But if you want it to act like an a tag and so you can do "./page", "#bottom" or "?a=567" use window.location.replace()
<select onChange="window.location.redirect(this.value)">
<option value="..">back</option>
<option value="./list">list</option>
<option value="#bottom">bottom</option>
</select>

Extending on #kevin's answer,
if someone has to perform some confirmation logic if URL is critical.
<select onChange=" this.options[this.selectedIndex].text == 'Delete' ? "Confirmation logic" : window.location.href=this.value;" >
<option selected disabled>Action</option>
<option value="/user/view">View</option>
<option value="/user/edit">Edit</option>
<option value="/user/delete">Delete</option>
</select>

You can use this code:
<select id="menu" name="links" size="1" onchange="window.location.href=this.value;">
<option value="URL">Book</option>
<option value="URL">Pen</option>
<option value="URL">Read</option>
<option value="URL">Apple</option>
</select>

Cascading Combo box HTML

I am not really a web person and am having trouble creating a cascading combo box. I have my options, but when I cannot figure out how to do a JavaScript command to switch the second box depending on the first box's selection.
These are my first set of options:
<select id="searchType" onchange="selectedOption(this)">
<option value="sessions">Sessions</option>
<option value="files">Files</option>
<option value="clients">Clients</option>
</select>
Depending on what they click there I would like to show these set of options:
SESSIONS
<select id="secondOptions">
<option value="conf">Config ID</option>
<option value="length">Length</option>
<option value="date">Date</option>
</select>
FILES
<select id="secondOptions">
<option value="id">File ID</option>
<option value="length">Length</option>
<option value="sent">Sent</option>
<option value="sessionId">Session ID</option>
</select>
CLIENTS
<select id="secondOptions">
<option value="name">Client Name</option>
<option value="organization">Organization</option>
<option value="specialty">Specialty</option>
<option value="sessionId">Session ID</option>
</select>
And finally a textbox to type into to really specify the search.
Once again, I am trying to do this using JavaScript, but if there is a better way to do this let me know please.

Given the amended html mark-up:
<form action="#" method="post">
<select id="searchType">
<option value="sessions">Sessions</option>
<option value="files">Files</option>
<option value="clients">Clients</option>
</select>
<select id="sessions">
<option value="conf">Config ID</option>
<option value="length">Length</option>
<option value="date">Date</option>
</select>
<select id="files">
<option value="id">File ID</option>
<option value="length">Length</option>
<option value="sent">Sent</option>
<option value="sessionId">Session ID</option>
</select>
<select id="clients">
<option value="name">Client Name</option>
<option value="organization">Organization</option>
<option value="specialty">Specialty</option>
<option value="sessionId">Session ID</option>
</select>
<fieldset id="textAreaSearchBox">
<legend>Search:</legend>
<textarea></textarea>
</fieldset>
</form>
(Note the changed ids, wrapping the form elements in a form, the addition of a fieldset, legend and textarea in the mark-up), the following JavaScript seems to work:
var select1 = document.getElementById('searchType');
var selects = document.getElementsByTagName('select');
select1.onchange = function() {
var select2 = this.value.toLowerCase();
for (i = 0; i < selects.length; i++) {
if (selects[i].id != this.id) {
selects[i].style.display = 'none';
}
}
document.getElementById(select2).style.display = 'block';
document.getElementById('textAreaSearchBox').style.display = 'block';
};
JS Fiddle demo.