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Trying to create quantity x cost with Javascript

I am creating a merchandise page where I have put the items into separate tables. I want to have it so that when someone selects a quantity, it will display the appropriate price in the field below. Here's the HTML so far:
<table border="1" id="tshirtTable" style="float:left">
<tr>
<th colspan="2">Burundi T-Shirt</th>
</tr>
<tr>
<td colspan="2"><img src="https://rlv.zcache.com/burundi_t_shirt-re5f84ff8b0724bbda7582389e5816a6f_k2g1o_324.jpg" alt="Burundi T-shirt"></td>
</tr>
<tr>
<td id="qty">Quantity</td>
<td>
<select id="tshirt">
<option value="0" selected>0</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
</td>
</tr>
<tr>
<td id="price">Price</td>
<td><input type="text" disabled="true"></td>
</tr>
</table>
I'm pretty new to JS so not sure how to have it calculate the price, depending on which quantity is selected. Guessing I'll have to set the price somewhere, but not exactly sure how to get started on it.
Any help is appreciated, thanks!

I've refactored your code. In my example, we have list of products. It doesn't really matter, you can have here one product or as many as you want. For learning purposes it's better do handle table of items.
First of all we won't be using disabled attribute but readonly. It's is very important, because disabled key-value won't be send to the server. If you want to block the input from changing use readonly. Secondly you don't need to pass =true value to your attribute.
<input type="text" disabled="true"> // bad
<input type="text" readonly> // ok
Another thing is that attribute id is unique per document and we can have only one. Read more on MDN.
The id global attribute defines a unique identifier (ID) which must be
unique in the whole document. Its purpose is to identify the element
when linking (using a fragment identifier), scripting, or styling
(with CSS).
No jQuery in my example, you should learn pure javascript first.
To calc, we must change type of our values. Reading them from inputs, their type is String, we must convert them to Number. In our case we use parseInt() function. It's better to use parseFloat(), when we expect floating point number.
Read my comments to have better understanding what is going on. If you have any confusion make sure to ask.
var table = document.getElementById('tshirtTable');
table.addEventListener("change", function(e) {
// If we are not changing these elements we quit
if (e.target.name !== 'quantity' && e.target.name !== 'each-price') {
return;
}
// Let's check what is id of our element
// We store our id in <tr id="..."
// To access tr, we must find tr by using .closest function
var tr = e.target.closest('tr');
var productId = tr.id;
var quantityValue = tr.querySelector('.quantity').value;
var eachPriceValue = tr.querySelector('.each-price').value;
var totalPriceValue = tr.querySelector('.total-price').value;
// Here is important part, we must parse values as type Number, because currently they are type String
tr.querySelector('.total-price').value = ( parseInt(quantityValue) * parseInt(eachPriceValue)).toFixed(2);
});
<table border="1" id="tshirtTable" style="float:left">
<thead>
<th>Name</th>
<th>Quantity</th>
<th>Price / Each</th>
<th>Total Price</th>
</thead>
<tbody>
<tr id="1">
<td>Burundi T-Shirt</td>
<td><select class="quantity" name="quantity">
<option value="0" selected>0</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
</td>
<td><input class="each-price" type="text" name="each-price" value="15"></td>
<td><input class="total-price" name="total-price" type="text" readonly></td>
</tr>
<tr id="2">
<td>Burundi Skirt</td>
<td><select class="quantity" name="quantity">
<option value="0" selected>0</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
</td>
<td><input class="each-price" type="text" name="each-price" value="25"></td>
<td><input class="total-price" name="total-price" type="text" readonly></td>
</tr>
<tr id="3">
<td>Burundi Mask</td>
<td><select class="quantity" name="quantity">
<option value="0" selected>0</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
</td>
<td><input class="each-price" type="text" name="each-price" value="30"></td>
<td><input class="total-price" name="total-price" type="text" readonly></td>
</tr>
</tbody>
</table>

First you have to add function which have to be call on document ready or as pure javascript document.onload()
Then you have to define a variable name for the price,
Then you have to get the value of your (#tishirt) and multiply it with the price get the result as a value for your text input in which the price display
Here is the script
<script type ="text/javascript">
document.onload=function(){
document.getElementById(#tishirt).onchange=function(){
var price=100 ;//only example price
var total=price*document.getElementById(#tishirt).value;
if (total>0){
document.getElementById(#total).value=total;
}
};
};
</script>
Don't forget to add id to your text box (#total)

Multiple textboxes fill the dropdown selection having same class in jquery

I have used the concept of multiple textboxes having same class fill with the multiple dropdown option selection which also having same class.I have facing problems in it.when i click the first dropdown option then it change the second textbox value.I want that if i click on first dropdown option it changes the values of first textbox not other or if click the second dropdown option it will change the value of second textbox.
<form action="" method="post">
<select name="drop[]" id="budget" class="drop">
<option value="1">option1</option>
<option value="2">option2</option>
<option value="3">option3</option>
</select>
<input type="text" name="txt" id="txt" class="txt" value="text1"><br>
<select name="drop[]" id="budget1" class="drop">
<option value="1">option1</option>
<option value="2">option2</option>
<option value="3">option3</option>
</select>
<input type="text" name="txt" id="txt1" class="txt" value="text2">
</form>
$('input[name="txt"]').each(function () {
$('.drop').on('change', function(){
var total = $(this).val();
$('input[name="txt"]').val($(this).find("option:selected").attr("value"));
});
});

You need to find out the next input element which should be updated when you change a select element. You can use the below code to achieve this.
$('.drop').on('change', function(){
var total = $(this).val();
$(this).next("input:first").val($(this).find("option:selected").attr("value"));
});
Plunker : https://plnkr.co/edit/qFjuFtwhHBvDE9zxAup2?p=preview

Dropdown box - onchange and onselect

I want help, i am very new to html..
On selecting option from dropdown menu, I want html to put the values in word..
e.g. When I select "1" from drop down, it must show "one"
When I select "2' from drop down, it must show "two"
How to do that??
<HTML>
<Table border=10>
<TR>
<TD>Select Number</TD>
<TD><Select>
<option>1</option>
<option>2</option>
<option>3</option>
</Select></TD>
</TR>
<tr>
<td>In Words</td>
<td><input type="text" readonly></td>
</tr>
</Table>
</HTML>
Please make a script and show me...

A non-jQuery solution:
Firstly, give your select- and input-tags id's, and your options values (value=""). Then add a onchange=""-listener in the select-tag and make a function that carries out what you want to do (i.e. checking the selected value and displaying it in your input field), like so:
function showValue() {
var x = document.getElementById("mySelect").value;
document.getElementById("mySelection").value = "You selected: " + x;
}
<Table border=10>
<tr>
<td>Select Number</td>
<td><Select onchange="showValue()" id="mySelect">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</Select></td>
</tr>
<tr>
<td>In Words</td>
<td><input type="text" id="mySelection"></td>
</tr>
</Table>

If I understand what you want, you'll need some javascript to find what you selected, and take that 'string' and shove it in an element for the user to see.
Here is a working example. Try making one these next time you ask a question. Welcome to Stack Overflow.
http://jsfiddle.net/sheriffderek/6vp5Lskn/
HTML
<select name='my_select' id='my_select'>
<option value='1'>Option 1</option>
<option value='2'>Option 2</option>
<option value='3'>Option 3</option>
<option value='4'>Option 4</option>
<option value='5'>Option 5</option>
</select>
<div id="outcome">
You have selected: <span></span>
</div>
javascript (jQuery)
var selectedOption; // define this variable
// when the select is changed...
$('#my_select').on('change', function() {
// get the option that was selected
selectedOption = $( "#my_select option:selected" ).text();
// put the option in the place you want it
$('#outcome span').html(selectedOption);
});

Working with dropdownlistbox in html

I am using dropdownlist and one label in my html page. I want to change name of label
on selection of my dropdownlist box. How is it possible?
pls povide any help for me .

Check this example.
It will change the attribute 'name' of your label, and its text content (reading its new name attribute value) to see the change in effect.
<script type="text/javascript">
function changeValue(select) {
var value = select.options[select.selectedIndex].value;
var label = document.getElementById('mylabel');
label.setAttribute('name', value);
label.innerHTML = label.getAttribute('name');
}
</script>
<select name="selectcity" onchange="changeValue(this);" >
<option>Mumbai</option>
<option>Delhi</option>
</select>
You selected: <label id="mylabel" name="citylabel"></label>

<select id='derp' onchange="changeVal(this,'changeme');"> <!-- declare select, set onchange to point to changeVal JS -->
<option value='test'>test</option>
</select>
<input id='changeme' />
<script type='text/javascript'>
function changeVal(el,changeElID){
var changeEl = document.getElementById(changeElID); // Get input to change
changeEl.value = el.options[el.selectedIndex].value; // Change input value to value of selected index
}
</script>
[EDIT]
re-reading the question it sounds like you are trying to change the name of the input box...if that is the case, change changeEl.value to changeEl.name

HTML:
<table cellspacing="0" cellpadding="1" rules="all" border="0" id="gvLanguage">
<tr>
<td align="left">
<select id="ddlLanguage" style="width: 230px;">
<option value="0">[Select]</option>
<option value="1">Afrikaans</option>
<option value="2">Akan</option>
<option value="3">Albanian</option>
<option value="4">American</option>
</select>
</td>
</tr>
<tr>
<td>
Selected Value: <label id="lblChange" ></label>
</td>
</tr>
</table>
JQUERY:
$(document).ready(function(){
$("#ddlLanguage").change(function(){
var vSelectedValue = $("option:selected",$(this)).text();
$("#lblChange").text(vSelectedValue);
});
});
CLICK HERE TO SEE THE DEMO

How to pass parameters on onChange of html select

I am a novice at JavaScript and jQuery. I want to show one combobox-A, which is an HTML <select> with its selected id and contents at the other place on onChange().
How can I pass the complete combobox with its select id, and how can I pass other parameters on fire of the onChange event?

function getComboA(selectObject) {
var value = selectObject.value;
console.log(value);
}
<select id="comboA" onchange="getComboA(this)">
<option value="">Select combo</option>
<option value="Value1">Text1</option>
<option value="Value2">Text2</option>
<option value="Value3">Text3</option>
</select>
The above example gets you the selected value of combo box on OnChange event.

Another approach wich can be handy in some situations, is passing the value of the selected <option /> directly to the function like this:
function myFunction(chosen) {
console.log(chosen);
}
<select onChange="myFunction(this.options[this.selectedIndex].value)">
<option value="1">Text 1</option>
<option value="2">Text 2</option>
</select>

For how to do it in jQuery:
<select id="yourid">
<option value="Value 1">Text 1</option>
<option value="Value 2">Text 2</option>
</select>
<script src="jquery.js"></script>
<script>
$('#yourid').change(function() {
alert('The option with value ' + $(this).val() + ' and text ' + $(this).text() + ' was selected.');
});
</script>
You should also know that Javascript and jQuery are not identical. jQuery is valid JavaScript code, but not all JavaScript is jQuery. You should look up the differences and make sure you are using the appropriate one.

JavaScript Solution
<select id="comboA">
<option value="">Select combo</option>
<option value="Value1">Text1</option>
<option value="Value2">Text2</option>
<option value="Value3">Text3</option>
</select>
<script>
document.getElementById("comboA").onchange = function(){
var value = document.getElementById("comboA").value;
};
</script>
or
<script>
document.getElementById("comboA").onchange = function(evt){
var value = evt.target.value;
};
</script>
or
<script>
document.getElementById("comboA").onchange = handleChange;
function handleChange(evt){
var value = evt.target.value;
};
</script>

I found #Piyush's answer helpful, and just to add to it, if you programatically create a select, then there is an important way to get this behavior that may not be obvious. Let's say you have a function and you create a new select:
var changeitem = function (sel) {
console.log(sel.selectedIndex);
}
var newSelect = document.createElement('select');
newSelect.id = 'newselect';
The normal behavior may be to say
newSelect.onchange = changeitem;
But this does not really allow you to specify that argument passed in, so instead you may do this:
newSelect.setAttribute('onchange', 'changeitem(this)');
And you are able to set the parameter. If you do it the first way, then the argument you'll get to your onchange function will be browser dependent. The second way seems to work cross-browser just fine.

jQuery solution
How do I get the text value of a selected option
Select elements typically have two values that you want to access.
First there's the value to be sent to the server, which is easy:
$( "#myselect" ).val();
// => 1
The second is the text value of the select.
For example, using the following select box:
<select id="myselect">
<option value="1">Mr</option>
<option value="2">Mrs</option>
<option value="3">Ms</option>
<option value="4">Dr</option>
<option value="5">Prof</option>
</select>
If you wanted to get the string "Mr" if the first option was selected (instead of just "1") you would do that in the following way:
$( "#myselect option:selected" ).text();
// => "Mr"
See also
.val() jQuery API Documentation

This is helped for me.
For select:
$('select_tags').on('change', function() {
alert( $(this).find(":selected").val() );
});
For radio/checkbox:
$('radio_tags').on('change', function() {
alert( $(this).find(":checked").val() );
});

You can try bellow code
<select onchange="myfunction($(this).val())" id="myId">
</select>

Html template:
<select class="staff-select">
<option value="">All</option>
<option value="196">Ivan</option>
<option value="195">Jon</option>
</select>
Js code:
const $staffSelect = document.querySelector('.staff-select')
$staffSelect.onchange = function () {
console.log(this.value)
}

Just in case someone is looking for a React solution without having to download addition dependancies you could write:
<select onChange={this.changed(this)}>
<option value="Apple">Apple</option>
<option value="Android">Android</option>
</select>
changed(){
return e => {
console.log(e.target.value)
}
}
Make sure to bind the changed() function in the constructor like:
this.changed = this.changed.bind(this);

this code once i write for just explain onChange event of select you can save this code as html and see output it works.and easy to understand for you.
<html>
<head>
<title>Register</title>
</head>
<body>
<script>
function show(){
var option = document.getElementById("category").value;
if(option == "Student")
{
document.getElementById("enroll1").style.display="block";
}
if(option == "Parents")
{
document.getElementById("enroll1").style.display="none";
}
if(option == "Guardians")
{
document.getElementById("enroll1").style.display="none";
}
}
</script>
<form action="#" method="post">
<table>
<tr>
<td><label>Name </label></td>
<td><input type="text" id="name" size=20 maxlength=20 value=""></td>
</tr>
<tr style="display:block;" id="enroll1">
<td><label>Enrollment No. </label></td>
<td><input type="number" id="enroll" style="display:block;" size=20 maxlength=12 value=""></td>
</tr>
<tr>
<td><label>Email </label></td>
<td><input type="email" id="emailadd" size=20 maxlength=25 value=""></td>
</tr>
<tr>
<td><label>Mobile No. </label></td>
<td><input type="number" id="mobile" size=20 maxlength=10 value=""></td>
</tr>
<tr>
<td><label>Address</label></td>
<td><textarea rows="2" cols="20"></textarea></td>
</tr>
<tr >
<td><label>Category</label></td>
<td><select id="category" onchange="show()"> <!--onchange show methos is call-->
<option value="Student">Student</option>
<option value="Parents">Parents</option>
<option value="Guardians">Guardians</option>
</select>
</td>
</tr>
</table><br/>
<input type="submit" value="Sign Up">
</form>
</body>
</html>

function setMyValue(v) {
console.log(v);
}
<select onchange="setMyValue(this.value)">
<option value="a">1</option>
<option value="b">2</option>
<option value="c">3</option>
</select>

This worked for me onchange = setLocation($(this).val())
Here.
#Html.DropDownList("Demo",
new SelectList(ViewBag.locs, "Value", "Text"),
new { Class = "ddlStyle", onchange = "setLocation($(this).val())" });

Simply:
function retrieve(){
alert(document.getElementById('SMS_recipient').options[document.getElementById('SMS_recipient').selectedIndex].text);
}
function retrieve_other() {
alert(myForm.SMS_recipient.options[document.getElementById('SMS_recipient').selectedIndex].text);
}
function retrieve() { alert(document.getElementById('SMS_recipient').options[document.getElementById('SMS_recipient').selectedIndex].text);
}
<HTML>
<BODY>
<p>RETRIEVING TEXT IN OPTION OF SELECT </p>
<form name="myForm" action="">
<P>Select:
<select id="SMS_recipient">
<options value='+15121234567'>Andrew</option>
<options value='+15121234568'>Klaus</option>
</select>
</p>
<p>
<!-- Note: Despite the script engine complaining about it the code works!-->
<input type="button" onclick="retrieve()" value="Try it" />
<input type="button" onclick="retrieve_other()" value="Try Form" />
</p>
</form>
</HTML>
</BODY>
Output:
Klaus or Andrew depending on what the selectedIndex is. If you are after the value just replace .text with value. However if it is just the value you are after (not the text in the option) then use document.getElementById('SMS_recipient').value

//html code
<select onchange="get(this)">
<option value="a">1</option>
<option value="b">2</option>
<option value="c">3</option>
</select>
//javscript code
function get(select) {
let value = select.value;
console.log(value);
}