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It seems onChange="myFunction()" is only calling my function once?

I have the following HTML that is within a form, to accept 2 numbers from two separate inputs
<input type="number" id="amount" name="amount" value="0" onchange="ltv()">
<input type="number" id="property_value" name="property_value" value="0" onchange="ltv()">
<p id="ltv"></p>
Then some JavaScript
function ltv() {
var amount = document.getElementById("amount").textContent;
var property_value = document.getElementById("property_value").textContent;
document.getElementById("ltv").innerHTML = Math.round(amount/property_value*100);
};
However after entering a number into the "amount" input the ltv element is updated with NaN which is to be expected at this stage as only the first variable in the math operation is set, however upon entering the second number and tabbing away from the input field the ltv is not updated again.

Seems like textContent isn't returning anything. Try to use .value
function ltv() {
var amount = document.getElementById("amount").value;
var property_value = document.getElementById("property_value").value;
document.getElementById("ltv").innerHTML = Math.round(amount/property_value*100);
};

Django - Get "total" between two elements in HTML in real-time using a script

I know this question has being done here a lot but I looked and tried a lot of answers, wasn't able to retrieve what i need.
First, I pass a value from an item using django forms through the view. In this example, the template receive the value of "900" because I use the default {{form.price}} in HTML .
<input type="text" name="price" value="900" readonly="readonly" id="id_price">
Inside the same HTML i have a field to manually insert a quantity:
<input type="text" name="quantity" id="quantity">
And the final input to show to multiplication between those two
<input type="text" name="total" id="total">
As a script I used this (saw the answer in a question but i wasn't able to recreate the result in my "total" input)
SCRIPT
<script>
$(document).ready(function () {
$('').keyup(function () {
var multiplyAndShow = function () {
var val1 = parseFloat($('#id_price').val())
var val2 = parseFloat($('#quantity').val())
val3 = val1 * val2 || "Some Text"
$("#total").html(val3)
}
$("#id_price").keyup(function () { multiplyAndShow(); });
$("#quantity").keyup(function () { multiplyAndShow(); });
});
});
</script>
The script is not been used because when I set a quantity it doesn't make a thing in real time. The price value is readonly so i don't know if that's the problem.
I'm a newbie in javascript so any help will be appreciated

You should set the value of the total field, not the html. Change the following line
$("#total").html(val3)
to
$("#total").val(val3)
You should also change the $('') to $(document).

How to calculate the total value of a dynamic number of fields using javascript?

My page shows some forms with content loaded from a database. Every row will get his own <input>. The ID of this input is equal for every row, except for the number that is attached to it, to make it unique. To make it more clear; this is how the form looks like when it loads 3 rows from the database:
<form>
<input id="Amount1" value="<?php echo $databaseValue; ?>" >
<input id="Amount2" value="<?php echo $databaseValue; ?>" >
<input id="Amount3" value="<?php echo $databaseValue; ?>" >
<input type="hidden" name="numberOfRows">
<input id="finalResult">
</form>
This is all done with the mysqli_array function. The value of numberOfRows is based on numRows function.
What I'd like to achieve is that javascript calculates the value of each existing input and put the result in finalResult, regardless the number of forms (because this may vary). If I make some changes to one of the values, the finalResult should update real-time.
What I've tried so far:
formnum contains the number of fields.
var a is created at the beginning, starting at 0. Inside it's function I create an ID, matching the fields on the page. All fields are named "Amount" + number. If this number equals the number of fields, the function will stop. This way the script won't be looking for fields that doesn't excist.
Then it gets the value of this field and adds the value to var b. var b is just created to store the value temporary, untill the function's over.
At the end the total is divided to 15. This is something extra I need. Nothing special on this line.
My code:
<script type='text/javascript'>
$(document).ready(function(){
var formnum = $("#numberOfRows").val();
var a;
var b = 0;
var formname = '#Amount';
for (a = 0; a < formnum; a++) {
var complete = formname.concat(a);
var completeContent = $(complete).val();
b = b + completeContent;
};
b = b.toFixed(2);
});
$(document).mousemove(function(event){
var formula_finalResult = b / 15;
var total_finalResult = Math.floor(formula_finalResult);
$("#finalResult").val(total_finalResult);
});
</script>
This doesn't do anything. It doesn't change the value. What's going wrong?

Make it simple:
$(function(){
var sum = 0;
// Selector to select all input whose id starts with Amount
$("input[id*='Amount']").each(function(){
sum += +$(this).val(); // Parsing as int and adding it to sum
});
$("#finalResult").val(Math.floor(sum/15)); // Storing the values
})

Assuming that all of the fields always have Amount at the beginning of their id attribute, you could use jQuery's ID selector to achieve this, without the need for any of the internal counters, etc.
I'm not entirely sure why you need to hook into the mousemove event, since the data should never change on the page (since it's being generated by PHP when the page is first loaded). The following code should achieve what you're looking for:
$(function() {
var total = 0;
$('input[id*="Amount"]').each(function() { total+= parseFloat( $(this).val() ); });
$('#finalResult').val( Math.floor( total / 15 ) );
});

Your code has an error Uncaught ReferenceError: b is not defined
see it in action here: http://jsfiddle.net/ca9vascj/
There's no reason to bring the mousemove event into this, I'm not even sure what that was needed for.
Like the above answers, here's a much simplified version. But instead of a partial ID selection, let's just give the form an ID, and then give all the needed elements inside that form a class that we can select by. We also no longer need to have the numberOfRows form element.
<form id="theForm">
<input class="formAmmount" value="5" />
<input class="formAmmount" value="10" />
<input class="formAmmount" value="27.5" />
<input class="formAmmount" value="4" />
<input class="formAmmount" value="9" />
<hr />
<input id="finalResult" />
</form>
And then our jQuery code can be reduced to this:
$(function(){
var total = 0;
$("#theForm .formAmmount").each(function(){
total += parseFloat(this.value, 10);
});
var final = Math.floor(total.toFixed(2) / 15);
$("#finalResult").val(final);
});
See it in action here: http://jsfiddle.net/ca9vascj/1/

You dont'need jQuery. The simplest way to do this is document.getElementsByTagName:
var inputs = document.getElementById('my-form').getElementsByTagName('input')
That's it. inputs.length will always get an actual count of inputs in your form. That's because getElementsByTagName() returns a NodeList object, containing a live view of the matching elements. This object is mutable; it will change in response to DOM mutations.
So if you need to get sum from all of the inputs:
function sum() {
var result = 0;
[].slice.call(inputs).forEach(function(input){
result += parseFloat(input.value)
});
return result;
}

If you are able to change the generated Html-Source I would suggest to give a new class to your InputElements.
<input id="Amount1" class="ElementToCount" value="<?php echo $databaseValue; ?>" >
Then you can calculate like that
var getSumOfElements = function() {
var Elements = $('.ElementToCount')
var sum=0
if (Elements && Elements.length>0) {
for (var i=0; i<Elements.length; i++) {
sum += Elements[i].val();
}
}
return sum
}
And to update the field you could register to the 'change'-Event
$('.ElementToCount).on('change', function() {
$('#finalResult').val(getSumOfElements());
})

Javascript function adding checkboxes to a total number?

I have a function where I'm trying to add the total number of checkboxes ticked to a value that is already displayed in the textbox. The solution I have works but it doesn't update properly if I uncheck the boxes and click total again.
Is there a way I can fix this so that the textbox updates accordingly?
HTML
<td><input type="text" name="Yeses" id="NumberofRisks" class = "form-control" value ="<?php echo $row['Total-Score'];?> " style = "width:50px"></td>
Javascript
function sum()
{
sumField = document.getElementById("NumberofRisks");
var sum = sumField.value;
$("input[name^='yanswer']:checked").each(function(){
sum++;
});
sumField.value = sum;
}

You are updating the value of the input after every call to function sum().
Instead have the initial sum value.
Then every time use this value.
var initial = $("#NumberofRisks").val();
function sum()
{
$("#NumberofRisks").val(initial + $("input[name^='yanswer']:checked").length);
displayRating($("#NumberofRisks").val());
}

Keep the original value of the textbox in a variable. Add an event listener to the checkboxes that count the number of checked boxes and adds that number to the original value, then updates the textbox.
Something like this:
HTML:
<input type="checkbox" class="check" />
<input type="checkbox" class="check" />
<input type="checkbox" class="check" />
<input type="textbox" class="text" />
JS:
//Store the original value. The 5 here should be whatever was supposed to be in the textbox.
var originalValue = 5;
$('.text').val(originalValue);
$('.check').on('change', function() {
//Count the number of checked boxes and add it to the original value for display.
var checked = $('.check:checked').length;
$('.text').val(originalValue+checked);
});
Here's a fiddle.

Calculate one variable based on changing input

I have the following function:
function updateInput(ish){
document.getElementById("BetAmount").value = ish;
}
I have the following HTML inputs:
<input class="defaultText" type="number" name="BetAmount" id="BetAmount" onchange="updateInput(this.value)">
<input type="number" name="PotentialGain" id="PotentialGain" />
When users enter in a bet amount number(BetAmount), I would like to instantly show a calculated PotentialGain, which, for example, can be found by multiplying a constant by the specified bet amount entered in by the user.
I'm not very familiar with JavaScript, so any help is greatly appreciated!

Your code is almost correct - you are showing the result in the BetAmount field so no change is visible.
Change your code to:
document.getElementById("PotentialGain").value = ish;
Here's a working demo. I changed the event to onkeyup as onchange only happens on blur - i.e. when a field loses focus.

Here is the final JQuery function that I used.
function changeBet(bet) {
var moneyline = <?php echo json_encode($win) ?>;
var gain = moneyline * bet;
document.getElementById("PotentialGain").value = gain;
}
Along with these inputs:
<input type="text" name="BetAmount[]" id="BetAmount" onkeyup="changeBet(this.value);" >
<input type="number" name="PotentialGain" id="PotentialGain" />