Develop Reference

I want to add new data from second table to main table

I want to add new data to the main table using the checkbox option, but the data added is not the same as the selected data. this is my code ...
<table border="1" id="table2">
<tr>
<td>Raka</td>
<input type="hidden" id="fname" value="Raka">
<td>Gilbert</td>
<input type="hidden" id="lname" value="Gilbert">
<td><input type="checkbox" name="chk"></td>
</tr>
<tr>
<td>Achyar</td>
<input type="hidden" id="fname" value="Achyar">
<td>Lucas</td>
<input type="hidden" id="lname" value="Lucas">
<td><input type="checkbox" name="chk"></td>
</tr>
</table>
<script>
$(document).on('click', '#Add', function() {
$("table").find('input[name="chk"]').each(function(){
if($(this).is(":checked")){
var fname = $('#fname').val();
var lname = $('#lname').val();
var newData = '<tr>'+
'<td>'+fname+'</td>'+
'<td>'+lname+'</td>'+
'<tr>';
$('table').append(newData);
}
});
})
</script>

You need to change your id="fname" to class="fname" and get the input value closest to checkbox. Currently you are getting data from the first inputs as they have the same id's.
function valueExists(value) {
if (!value) {
return true;
}
let exists = false;
$("#main-table").find('tr').each(function() {
let fname = $(this).find("td:nth-child(1)").text(),
lname = $(this).find("td:nth-child(2)").text();
const fullName = `${fname}${lname}`;
if (value.toLowerCase() === fullName.toLowerCase()) {
exists = true;
}
});
return exists;
}
$(document).on('click', '#add', function() {
$("table").find('input[name="chk"]').each(function(e) {
if ($(this).is(":checked")) {
var fname = $(this).parents('tr').find('.fname').val();
var lname = $(this).parents('tr').find('.lname').val();
if (valueExists(`${fname}${lname}`)) return;
var newData = '<tr>' +
'<td>' + fname + '</td>' +
'<td>' + lname + '</td>' +
'<tr>';
$('#main-table').append(newData);
}
});
})
<link href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" rel="stylesheet"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<h1>Main Table</h1>
<table class="table table-dark" border="1" id="main-table">
</table>
<hr>
<h1>Second table</h1>
<table border="1" id="table2">
<tr>
<td class="name">Raka</td>
<input type="hidden" class="fname" value="Raka">
<td class="last">Gilbert</td>
<input type="hidden" class="lname" value="Gilbert">
<td><input class="check" type="checkbox" name="chk"></td>
</tr>
<tr>
<td class="name">Achyar</td>
<input type="hidden" class="fname" value="Achyar">
<td class="last">Lucas</td>
<input type="hidden" class="lname" value="Lucas">
<td><input class="check" type="checkbox" name="chk"></td>
</tr>
</table>
<button type="button" id="add" name="button">Add</button>

Try this. I have used plain javascript
document.addEventListener("click", function() {
[...document.querySelectorAll("input[name='chk']")].forEach(data => {
console.log(data);
if (data.checked) {
const fname = document.getElementById("fname").value;
const lname = document.getElementById("lname").value;
const newData = `<tr><td>${ fname }</td><td>${ lname }</td</tr>`;
// "<tr>" + "<td>" + fname + "</td>" + "<td>" + lname + "</td>" + "<tr>";
document.getElementById("table2").innerHTML += newData;
}
});
});
Hope was useful. If any flaws please update

Here is a neater solution, using 2 tables as requested, without hidden inputs and a better use of 'tables' and 'trs' in jquery
$(function(){
$("#btnAdd").click(function(){
let table1 = $("#table1");
table2 = $("#table2");
$.each(table2.find('tr'), function(i, tr){
tr = $(tr);
let new_tr = $('<tr>');
if (tr.find("td input").is(":checked")) {
let fname = tr.find("td:nth-child(1)").html(),
lname = tr.find("td:nth-child(2)").html();
new_tr.append(
'<td>' + fname + '</td>' +
'<td>' + lname + '</td>' +
'<td><input type="checkbox" name="chk"></td>'
);
table1.append(new_tr)
}
})
});
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
TABLE 1
<table border="1" id="table1">
</table>
<hr/>
TABLE 2
<table border="1" id="table2">
<tr>
<td>Raka</td>
<td>Gilbert</td>
<td><input type="checkbox" name="chk"></td>
</tr>
<tr>
<td>Achyar</td>
<td>Lucas</td>
<td><input type="checkbox" name="chk"></td>
</tr>
</table>
<button type="button" id="btnAdd">Add</button>

Javascript- Add row dynamically contain dropbox and formula

I have a table consist of 5 column: Code, Name, Qty, Price, and Total.
Code contain a dropbox menu which dynamically retrieve from another table. If user click the dropbox and select a code, name of the item will appear automatically in Name column.
For Total column, the value will appear from multiplying Qty and Price. The multiply script I used is:
<script language="javascript" type="text/javascript">
function multiply()
{
a=Number(document.calculator.qty.value);
b=Number(document.calculator.price.value);
c=a*b;
document.calculator.total.value=c;
}
</script>
My code for the table as below:
<table id="theTable" border="1">
<script>
var maxID = 0;
function getTemplateRow() {
var x = document.getElementById("templateRow").cloneNode(true);
x.id = "";
x.style.display = "";
x.innerHTML = x.innerHTML.replace(/{id}/, ++maxID);
return x;
}
function addRow() {
var t = document.getElementById("theTable");
var rows = t.getElementsByTagName("tr");
var r = rows[rows.length - 1];
r.parentNode.insertBefore(getTemplateRow(), r);
}
</script>
<thead>
<tr>
<th> Code </th>
<th> Name </th>
<th> Qty </th>
<th> Price </th>
<th> Total </th>
<tr>
</thead>
<tbody>
<tr id="templateRow">
<td type="text" name="code" id="code"/readonly>
<?php
mysql_connect("localhost","root","");
mysql_select_db("inventory");
$result = mysql_query("select * from input_code_data");
$jsArray = "var code = new Array();\n";
echo '<select name="code" onchange="changeValue(this.value)">';
echo '<option></option>';
while ($row = mysql_fetch_array($result)) {
echo '<option value="' . $row['code'] . '">' . $row['code'] . '</option>';
$jsArray .= "code['" . $row['code'] . "'] = {name:'" . addslashes($row['name']) . "',desc:'".addslashes($row['name'])."'};\n";
}
echo '</select>';
?>
</td>
<td><input type="text" name="name" id="name"/readonly>
<script type="text/javascript">
<?php echo $jsArray; ?>
function changeValue(id){
document.getElementById('code').value = code[id].name;
document.getElementById('name').value = code[id].desc;
};
</script>
</td>
<td><input type="text" name="qty"></td>
<td><input type="text" name="price"></td>
<td><input type="text" name="total" /readonly><INPUT type="button" value="Click" onclick="javascript:multiply();"></td>
</tr>
</tbody>
</table>
<INPUT type='button' value='+' onclick="addRow('theTable')" />
If I click add row, then a new row will appear and the format is right. The problem is, when I select a code (from the dropbox) in second row, the name appear in the first row instead, not in the second row. Another problem, Click button for multiply isn't working in the second row.
Would anybody tell me how I fix this? Thanks.

It's because your changeValue(id) function is being called with the select field's value, not the row Id. Additionally, you're getting element by static id's instead of passing them in. HTML assumes that an Id will only appear once per page, you're breaking that so it always returns the first match.
EDIT for some example code:
This deals with some of the issues (if I'm understanding you properly). You might find the MDN docs helpful around how ids and other selectors work.
multiply suffers from the same issues as your original code, but you should be able to figure it out based on what is below:
<table id="theTable" border="1">
<thead>
<tr>
<th> Code </th>
<th> Name </th>
<th> Qty </th>
<th> Price </th>
<th> Total </th>
<tr>
</thead>
<tbody>
<tr class="templateRow" id="invoice-line-1">
<td class="code">
<select onchange="changeValue(this.value, 'invoice-line-1')">
<option value="1">Option 1</option>
<option value="2">Option 2</option>
<!-- etc. -->
</select>
<span></span>
</td>
<td class="name"></td>
<td><input type="text" name="qty"></td>
<td><input type="text" name="price"></td>
<td>
<input type="text" name="total" /readonly>
<input type="button" value="Click" onclick="javascript:multiply();">
</td>
</tr>
</tbody>
</table>
<input type='button' value='+' onclick="addRow('theTable')" />
<script type="text/javascript">
var codes = {
"1": {value: 1, name: "Option 1"},
"2": {value: 2, name: "Option 2"},
// etc.
},
numRows = 1;
function changeValue(value, id){
document.querySelector('#' + id + ' td.name').innerHTML = codes[value].name;
document.querySelector('#' + id + ' td.code > span').innerHTML = code[value].value;
};
function addRow() {
var newRow = document.getElementById("invoice-line-1").cloneNode(true),
table = document.querySelector("#theTable > tbody");
newRow.id = "invoice-line-" + (numRows = numRows + 1);
table.appendChild(rewRow);
document.querySelector("#invoice-line-" + numRows + " .code > select").setAttribute('onchange', "changeValue(this.value, 'invoice-line-" + numRows + "')");
}
</script>

Jquery .on(change) event on <select> input only changes first row.

I have a table whereby people can add rows.
There is a select input in the table that when changed, changes the values in a second select field via ajax.
The problem I have is that if a person adds an additional row to the table, the .on(change) event alters the second field in the first row, not the subsequent row.
I've been racking my brain, trying to figure out if I need to (and if so how to) dynamically change the div id that the event binds to and the div that it affects. Is this the solution? If so, could someone please demonstrate how I'd achieve this?
The HTML form is
<form action="assets.php" method="post">
<button type="button" id="add">Add Row</button>
<button type="button" id="delete">Remove Row</button>
<table id="myassettable">
<tbody>
<tr>
<th>Asset Type</th>
<th>Manufacturer</th>
<th>Serial #</th>
<th>MAC Address</th>
<th>Description</th>
<th>Site</th>
<th>Location</th>
</tr>
<tr class="removable">
<!--<td><input type="text" placeholder="First Name" name="contact[0][contact_first]"></td>
<td><input type="text" placeholder="Surname" name="contact[0][contact_surname]"></td>-->
<td><select name="asset[0][type]">
<option><?php echo $typeoption ?></option>
</select></td>
<td><select class="manuf_name" name="asset[0][manuf]">
<option><?php echo $manufoption ?></option>
</select></td>
<td><input type="text" placeholder="Serial #" name="asset[0][serial_num]"></td>
<td><input type="text" placeholder="Mac Address" name="asset[0][mac_address]"></td>
<td><input type="text" placeholder="Name or Description" name="asset[0][description]"></td>
<td><select id="site" name="asset[0][site]">
<option><?php echo $siteoption ?></option>
</select></td>
<td><input type="text" placeholder="e.g Level 3 Utility Room" name="asset[0][location]"></td>
<td><select id="new_select" name="asset[0][contact]"></select></td>
<!--<td><input type="email" placeholder="Email" name="contact[0][email]"></td>
<td><input type="phone" placeholder="Phone No." name="contact[0][phone]"></td>
<td><input type="text" placeholder="Extension" name="contact[0][extension]"></td>
<td><input type="phone" placeholder="Mobile" name="contact[0][mobile]"></td>-->
</tr>
</tbody>
</table>
<input type="submit" value="Submit">
<input type="hidden" name="submitted" value="TRUE" />
</form>
The script I have is
<script type="text/javascript">
$(document).ready(function() {
$("#add").click(function() {
var newgroup = $('#myassettable tbody>tr:last');
newgroup
.clone(true)
.find("input").val("").end()
.insertAfter('#myassettable tbody>tr:last')
.find(':input')
.each(function(){
this.name = this.name.replace(/\[(\d+)\]/,
function(str,p1) {
return '[' + (parseInt(p1,10)+1)+ ']'
})
})
return false;
});
});
$(document).ready(function() {
$("#delete").click(function() {
var $last = $('#myassettable tbody').find('tr:last')
if ($last.is(':nth-child(2)')) {
alert('This is the only one')
} else {
$last.remove()
}
});
});
$(document).ready(function() {
$("#myassettable").on("change","#site",function(event) {
$.ajax ({
type : 'post',
url : 'assetprocess.php',
data: {
get_option : $(this).val()
},
success: function (response) {
document.getElementById("new_select").innerHTML=response;
}
})
});
});
</script>
and the assetprocess.php page is
<?php
if(isset($_POST['get_option'])) {
//Get the Site Contacts
$site = $_POST['get_option'];
$contact = "SELECT site_id, contact_id, AES_DECRYPT(contact_first,'" .$kresult."'),AES_DECRYPT(contact_surname,'" .$kresult."') FROM contact WHERE site_id = '$site' ORDER BY contact_surname ASC";
$contactq = mysqli_query($dbc,$contact) or trigger_error("Query: $contact\n<br />MySQL Error: " .mysqli_errno($dbc));
if ($contactq){
//$contactoption = '';
echo '<option>Select a Contact (Optional)</option>';
while ($contactrow = mysqli_fetch_assoc($contactq)) {
$contactid = $contactrow['contact_id'];
$contactfirst = $contactrow["AES_DECRYPT(contact_first,'" .$kresult."')"];
$contactsurname = $contactrow["AES_DECRYPT(contact_surname,'" .$kresult."')"];
$contactoption .= '<option value="'.$contactid.'">'.$contactsurname.', '.$contactfirst.'</option>';
echo $contactoption;
}
}
exit;
}
?>
The code is ugly as sin, but this is only a self-interest project at this stage.
Any assistance would be greatly appreciated.
Cheers,
J.

Working Example: https://jsfiddle.net/Twisty/1c98Ladh/3/
A few minor HTML changes:
<form action="assets.php" method="post">
<button type="button" id="add">Add Row</button>
<button type="button" id="delete">Remove Row</button>
<table id="myassettable">
<tbody>
<tr>
<th>Asset Type</th>
<th>Manufacturer</th>
<th>Serial #</th>
<th>MAC Address</th>
<th>Description</th>
<th>Site</th>
<th>Location</th>
</tr>
<tr class="removable">
<td>
<select name="asset[0][type]">
<option>---</option>
<option>Type Option</option>
</select>
</td>
<td>
<select class="manuf_name" name="asset[0][manuf]">
<option>---</option>
<option>
Manuf Option
</option>
</select>
</td>
<td>
<input type="text" placeholder="Serial #" name="asset[0][serial_num]">
</td>
<td>
<input type="text" placeholder="Mac Address" name="asset[0][mac_address]">
</td>
<td>
<input type="text" placeholder="Name or Description" name="asset[0][description]">
</td>
<td>
<select id="site-0" class="chooseSite" name="asset[0][site]">
<option>---</option>
<option>
Site Option
</option>
</select>
</td>
<td>
<input type="text" placeholder="e.g Level 3 Utility Room" name="asset[0][location]">
</td>
<td>
<select id="new-site-0" name="asset[0][contact]">
</select>
</td>
</tr>
</tbody>
</table>
<input type="submit" value="Submit">
<input type="hidden" name="submitted" value="TRUE" />
</form>
This prepares the id to be incrementd as we add on new elements. Making use of the class, we can bind a .change() to each of them.
$(document).ready(function() {
$("#add").click(function() {
var newgroup = $('#myassettable tbody>tr:last');
newgroup
.clone(true)
.find("input").val("").end()
.insertAfter('#myassettable tbody>tr:last')
.find(':input')
.each(function() {
this.name = this.name.replace(/\[(\d+)\]/,
function(str, p1) {
return '[' + (parseInt(p1, 10) + 1) + ']';
});
});
var lastId = parseInt(newgroup.find(".chooseSite").attr("id").substring(5), 10);
newId = lastId + 1;
$("#myassettable tbody>tr:last .chooseSite").attr("id", "site-" + newId);
$("#myassettable tbody>tr:last select[id='new-site-" + lastId + "']").attr("id", "new-site-" + newId);
return false;
});
$("#delete").click(function() {
var $last = $('#myassettable tbody').find('tr:last');
if ($last.is(':nth-child(2)')) {
alert('This is the only one');
} else {
$last.remove();
}
});
$(".chooseSite").change(function(event) {
console.log($(this).attr("id") + " changed to " + $(this).val());
var target = "new-" + $(this).attr('id');
/*$.ajax({
type: 'post',
url: 'assetprocess.php',
data: {
get_option: $(this).val()
},
success: function(response) {
$("#" + target).html(response);
}
});*/
var response = "<option>New</option>";
$("#" + target).html(response);
});
});
Can save some time by setting a counter in global space for the number of Rows, something like var trCount = 1; and use that to set array indexes and IDs. Cloning is fast and easy, but it also means we have to go back and append various attributes. Could also make a function to draw up the HTML for you. Like: https://jsfiddle.net/Twisty/1c98Ladh/10/
function cloneRow(n) {
if (n - 1 < 0) return false;
var html = "";
html += "<tr class='removable' data-row=" + n + ">";
html += "<td><select name='asset[" + n + "][type]' id='type-" + n + "'>";
html += $("#type-" + (n - 1)).html();
html += "<select></td>";
html += "<td><select name='asset[" + n + "][manuf]' id='manuf-" + n + "'>";
html += $("#manuf-" + (n - 1)).html();
html += "<select></td>";
html += "<td><input type='text' placeholder='Serial #' name='asset[" + n + "][serial_num]' id='serial-" + n + "' /></td>";
html += "<td><input type='text' placeholder='MAC Address' name='asset[" + n + "][mac_address]' id='mac-" + n + "' /></td>";
html += "<td><input type='text' placeholder='Name or Desc.' name='asset[" + n + "][description]' id='desc-" + n + "' /></td>";
html += "<td><select name='asset[" + n + "][site]' class='chooseSite' id='site-" + n + "'>";
html += $("#site-" + (n - 1)).html();
html += "<select></td>";
html += "<td><input type='text' placeholder='E.G. Level 3 Utility Room' name='asset[" + n + "][location]' id='loc-" + n + "' /></td>";
html += "<td><select name='asset[" + n + "][contact]' id='contact-" + n + "'><select></td>";
html += "</tr>";
return html;
}
It's more work up front, yet offers a lot more control of each part. And much easier to use later.

Retrieving HTML Table Values

I created a table and borrowed a javascript function from http://www.fourfront.us/blog/store-html-table-data-to-javascript-array to retrieve the contents of the table the way I wanted to. It almost works, but for some reason I cannot access the value that the user inputs.
I have made a JS fiddle at http://jsfiddle.net/danielmdavies/4mu80x2L/1/
The code is also posted below. If I use "time_cutoff": $(tr).find('td:eq(2)').html() instead of "time_cutoff": $(tr).find('td:eq(2)').val(), I get the html code that is correct I believe.
This is the relevant html code:
<table id="cycler_table">
<tr>
<th>Cycle Step</th>
<th>Mode</th>
<th>Time Cutoff</th>
<th>Voltage Cutoff</th>
<th>Current Cuttoff</th>
</tr>
<tr>
<td>1</td>
<td>
<select name='cyc_mode1'>
<option value='galvanostatic'>Galvanostatic</option>
<option value='Potentiostatic'>Potentiostatic</option>
<option name='rest'>Rest</option>
</td>
<td>
<input type='text' name='time_cutoff1' value='10'>
</td>
<td>
<input type='text' name='voltage_cutoff1' value='0'>
</td>
<td>
<input type='text' name='current_cutoff1' value='0'>
</td>
</tr>
<tr>
<td>2</td>
<td>
<select name='cyc_mode2'>
<option value='galvanostatic'>Galvanostatic</option>
<option value='Potentiostatic'>Potentiostatic</option>
<option name='rest'>Rest</option>
</td>
<td>
<input type='text' name='time_cutoff2' value='10'>
</td>
<td>
<input type='text' name='voltage_cutoff2' value='0'>
</td>
<td>
<input type='text' name='current_cutoff2' value='0'>
</td>
</tr>
<tr>
<td>3</td>
<td>
<select name='cyc_mode3'>
<option value='galvanostatic'>Galvanostatic</option>
<option value='Potentiostatic'>Potentiostatic</option>
<option name='rest'>Rest</option>
</td>
<td>
<input type='text' name='time_cutoff3' value='10'>
</td>
<td>
<input type='text' name='voltage_cutoff3' value='0'>
</td>
<td>
<input type='text' name='current_cutoff3' value='0'>
</td>
</tr>
<tr>
<td>4</td>
<td>
<select name='cyc_mode4'>
<option value='galvanostatic'>Galvanostatic</option>
<option value='Potentiostatic'>Potentiostatic</option>
<option name='rest'>Rest</option>
</td>
<td>
<input type='text' name='time_cutoff4' value='10'>
</td>
<td>
<input type='text' name='voltage_cutoff4' value='0'>
</td>
<td>
<input type='text' name='current_cutoff4' value='0'>
</td>
</tr>
</table>
<textarea id="tbTableValuesArray" name="tblValuesArray" rows="10"></textarea>
</div>
<p id="cyc_confirm">Waiting for Properties to be Confirmed
<button onclick="storeAndShowTableValues()">Send the Setup</button>
And the Javascript
$(document).ready(function () {
console.log("ready!");
storeAndShowTableValues();
});
function storeAndShowTableValues() {
var TableData;
TableData = storeTblValues();
$('#tbTableValuesArray').val('TableData = \n' + print_r(TableData));
}
function storeTblValues() {
var TableData = new Array();
$('#cycler_table tr').each(function (row, tr) {
TableData[row] = {
"cyc_mode": $(tr).find('td').eq(1).val(),
"time_cutoff": $(tr).find('td:eq(2)').val(),
"voltage_cutoff": $(tr).find('td:eq(3)').val(),
"current_cutoff": $(tr).find('td:eq(4)').val()
}
});
TableData.shift(); // first row will be empty - so remove
return TableData;
}
function convertArrayToJSON() {
var TableData;
TableData = $.toJSON(storeTblValues());
$('#tbConvertToJSON').val('JSON array: \n\n' + TableData.replace(/},/g, "},\n"));
}
function print_r(arr, level) {
var dumped_text = "";
if (!level) level = 0;
//The padding given at the beginning of the line.
var level_padding = "";
for (var j = 0; j < level + 1; j++) level_padding += " ";
if (typeof (arr) == 'object') { //Array/Hashes/Objects
for (var item in arr) {
var value = arr[item];
if (typeof (value) == 'object') { //If it is an array,
dumped_text += level_padding + "'" + item + "' \n";
dumped_text += print_r(value, level + 1);
} else {
dumped_text += level_padding + "'" + item + "' => \"" + value + "\"\n";
}
}
} else { //Stings/Chars/Numbers etc.
dumped_text = "===>" + arr + "<===(" + typeof (arr) + ")";
}
return dumped_text;
}
This is probably super easy but for whatever reason I can't work out how to make it give me the values.
Any help would be awesome.

Try something like this to get the values:
TableData[row] = {
"cyc_mode": $(tr).find('select').val(),
"time_cutoff": $(tr).find('input:eq(0)').val(),
"voltage_cutoff": $(tr).find('input:eq(1)').val(),
"current_cutoff": $(tr).find('input:eq(2)').val()
};
You need to find the actual input and select elements to get their values.
Or better:
var elem = $(tr);
TableData[row] = {
"cyc_mode": elem.find('select').val(),
"time_cutoff": elem.find('input:eq(0)').val(),
"voltage_cutoff": elem.find('input:eq(1)').val(),
"current_cutoff": elem.find('input:eq(2)').val()
};
Which avoids recreating the jquery object four times.

Remove/delete part of hidden field value on button click

I am trying to build a form where users can add a course using select boxes.
When a course is added, it creates a new table row displaying the course to the user and also adds the course prefix and number (e.g. MATH120) to a hidden form field value. Finally, it adds a delete button.
The delete button should remove the table row AND the hidden input value that corresponds to the course being deleted.
Here's my jsfiddle: http://jsfiddle.net/MtJF2/10/
My script is deleting the row just fine, but its not removing the input value correctly. It's not throwing any errors. Sometimes I've noticed that it will delete the zero in the correct value (e.g. MATH120, becomes MATH12,). Any ideas what might be causing this?
HTML:
<script type="text/javascript">
function deleteCourse($course){
$('#' + $course).remove();
$course = $course + ','
alert($course);
$('#required-courses').val(function($course, value) {
return value.replace($course, '');
});
}
</script>
<table width="80%" align="center">
<tr id="add-required-course">
<td><input type="button" value="+ Add a Required Course" class="MC-big-button" onclick="$('#course-menu').slideToggle()" /></td>
</tr>
</table>
<input type="hidden" id="required-courses" name="required-courses" value="null" />
<table id="course-menu" width="80%" align="center">
<tr>
<td>Select the course prefix:</td>
<td><select id="1" name="course-prefix">
<option value="MATH">MATH</option>
<option value="BIOL">BIOL</option>
</select>
</td>
</tr>
<tr>
<td>Select the course number:</td>
<td><select id="2" name="course-num">
<option value="101">101</option>
<option value="120">120</option>
</select>
</td>
</tr>
<tr>
<td colspan="2">
<input type="button" value="Add this course" class="MC-big-button" id="save-course" />
</td>
</tr>
</table>
Javascript:
document.getElementById("save-course").onclick = buildCourse;
function buildCourse() {
var $coursePrefix = ($('#1').val());
var $courseNum = ($('#2').val());
var $course = $coursePrefix + $courseNum;
var $HTMLoutput = '<tr id="' + $course + '"><td>' + $course + '<input type="button" value="Delete" onclick="deleteCourse(\'' + $course + '\')" /></td></tr>';
var $VALUEoutput = ($('#required-courses').val());
if ($VALUEoutput == 'null') {
$VALUEoutput = $course + ',';
}
else {
$VALUEoutput = $VALUEoutput + $course + ',';
}
$('#course-menu').slideToggle();
$('#add-required-course').before($HTMLoutput);
$('#required-courses').val($VALUEoutput);
}
I found this question to be helpful, but I think my implementation is off.

You are replacing $course with a new value in the delete function at
$('#required-courses').val(function($course, value) {
// here it gets a new value which is wrong
Use it like this
function deleteCourse($course){
$('#' + $course).remove();
$course = $course + ','
alert($course);
$('#required-courses').val(function(_, value) {
return value.replace($course, '');
});
}