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Change Value of Gravity Form Field with JavaScript

I need to detect a change in a Gravity Form field (form 5, field 215; is a number field), round the number so I can get a trailing zero if it doesn't already have one, and then return the new, rounded value back to the field. I tried to piecemeal something together using bits of other code I found, but I must be doing something wrong. I'm an absolute rookie with JavaScript.
I'm using Gravity Wiz's "Gravity Forms Custom JavaScript" plugin to insert this script only on the page with the appropriate form.
jQuery(“#gform_fields_215”).on(“change”,”#input_215″, ( function(e) {
var number = document.getElementById("input_215");
var rounded = number.toFixed(2);
document.getElementById("input_215").value = rounded;
}
What am I doing wrong? Probably everything! LOL

I know you have already forgotten you ever asked this. but here's the solution.
jQuery('#gform_fields_215').on('change','#input_215', ( function(e) {
var number = document.getElementById("input_3_1_5").value;
var rounded = parseInt(number).toFixed(2);
document.getElementById("input_215").value = rounded;
}
You have used jQuery and vanilla js syntax. if you would use only jQuery it would be done as below.
jQuery("#gform_3").on("change", "#input_3_1_5", function (e) {
$(this).val(parseInt(this.value).toFixed(2));
});
element value is a string it need to be parsed into a number before adding decimal places
this.value can be used to get value of current element

How to always show the number prefix in html input field?

Is there any smart, minimalistic way to always show the prefix (positive, negative) of a number in a HMTL input field? (e.g. +1, 0, -1)
I have only found s solution for PHP:
How to prefix a positive number with plus sign in PHP
I have to use <input type="text"> since there are different implementations for text=number in different browsers: Localization of input type number
Why am I doing this?
I have an input field that shows the percentage that can be added (or subtracted) to a certain value.
Basevalue: 10
Mofification %: +10
Results: 11

The easiest way would be using some basic javascript. Add a script at the end of your HTML page (before the body closing tag) then give to the input an id, for example prefixedInput. Then you can write your little script
var inputField = document.getElementById("#prefixedInput");
var inputFieldValue = inputField.value;
if (inputFieldValue > 0) {
inputField.value = "+" + inputFieldValue;
}
if (inputFieldValue < 0) {
inputField.value = "-" + inputFieldValue;
}
Now, that works in a way that isn't really useful because this function will be executed just one time when the page will load, so if you have assigned to your input a value, this will be prefixed with its sign. However if you want to bind this behaviour to some actions (e.g. prefixing the value even if the user inserts the value after the intial page load) you will be forced in using event listeners.

Disallow typing after reaching input max length

I have a few inputs on my page that need to have a max length of sorts and this is working to an extent except that an extra number keeps being added because of a plugin we're using...and no I can't get rid of the plugin causing it.
To fix this I need to remove one character from the input field. I have gotten to the point where it will remove it from the value of the input, but it is still showing on the screen...which is the issue.
Is there a way to disallow typing after they hit a certain point using JavaScript? I cannot use max length in the case because the virtual keyboard we are using ignores that completely.
I have something like this
var target = event.currentTarget;
var name = $(target).attr("name");
var validationLength = $(target).attr("validation").length;
$('input[name="'+name+'"]').on('keyup keydown change', function () {
if($(this).val().length > validationLength){
$(this).val().substr(0,$(this).val().length-1);
};
});
And like I said this will remove it from the value of the input, but not what the user actually sees on the screen (the most important part). Any help would much appreciated!

validationLength = 10;
$('#test').on('keyup keydown change', function () {
if($(this).val().length > validationLength){
val=$(this).val().substr(0,$(this).val().length-1);
$(this).val(val);
};
});
http://jsfiddle.net/mctkpLph/

Slip input type value live using javascript

i'm trying to live edit a text box value so that the result will be split every two character,
adding a column and starting from some default character.
what i have till now is this code, that obviously doesn't work:
$('#textboxtext').keyup(function (){
var text = $("#textboxtext").val();
//$(text).attr('maxlength', '12');
var splitted = text.match(/.{2}|.{1,2}/g);
var result = ("B8:27:EB:" + splitted.join(':'));
});
i need the live split and the default character inside the textbox but i really don't know where to start...

From your code, it seems like you're trying to create a text box that has some very specific behavior. It looks like it needs to format its value in such a way that it always begins with certain 'prefix' of B8:27:EB:, and every subsequent pair of characters is is separated by a :. This is actually a very complex behavior and you have to consider a number of different interactions (e.g. what happens when the user attempts to delete or modify the prefix). I usually try to avoid such complex controls if possible, however here is a quick implementation:
$('#textboxtext').keyup(function (e){
var prefix = "B8:27:EB:",
text = $(this).val(),
splitted, result;
if (text.indexOf(prefix) == 0)
text = text.substr(9);
else if (prefix.indexOf(text) == 0)
text = "";
text = text.replace(/:/g, '');
splitted = text.match(/.{1,2}/g) || [];
result = prefix + splitted.join(':');
$(this).val(result);
});
Demonstration
Type inside the text box and see what happens. Also note, there are all kinds of interaction that this implementation doesn't account for (e.g. right-clicking and pasting into the text box), but it's a start.

How can I stop isNaN from returning an error for a blank field?

EDIT:
Ok so I'm updating this question, to show what I've built as I've still not been able to fix this issue. Here is an image of what I've got. So as you can see,
When the user enters a value, the calculation (they are just percentage and total calculations are done "onkeyup". As you can see because of this they return "NaN". Is there a way for me to stop the field displaying a NaN and then subsequently only showing the total values?
I have thought about this and I could just get all the fields to calculate as soon as something is input into the final field? What do you think. Apologies to all those that had perviously answered my question, I am still trying to figure out the best approach, I'm just not as good with JavaScript as I am with HTML/CSS!!

You should try writing a checkNumber function that takes the entered value as its argument (rather than referring directly to each field inside the function). Something like this:
var checkNumber = function (testval) {
if ( isNaN(testval) ) {
alert('Bad!');
// clean up field? highlight in red? etc.
} else {
// call your calculation function
}
}
Then bind that function to the keyup event of each form field. There are a number of ways to do this. Look into addEventListener(), or the binding features of a framework like jQuery (.delegate() or .keyup(), e.g.).
Note that if you do bind the function to the event, you won't have to explicitly pass in the value argument. You should be able to work with a field's value within the function via this.value. So you'd have something like this:
var checkNumber = function () {
if ( isNaN( this.value ) ) {
alert('Bad!');
// clean up field? highlight in red? etc.
} else {
// call your calculation function
}
}
And then (with a naive binding approach by ID):
document.getElementById('id_of_a_field').addEventListener('keyup', checkNumber, true);

Can't you just initialize the text box with a default value, say 0?

Why don't you use 3 different functions or an argument to identify which of the inputs the user is pressing? If each of the inputs calls checkNumber(1), checkNumber(2) and checkNumber(3) you can only validate the input that the user is using instead of validating all 3 at the same time.
Alternatively you can use input validation and instead of an alert just return false to prevent the user from inputing invalid chars

How about use short-circuit evaluation with jsFiddle example
EDIT for parseFloat:
function checkNumber()
{
var sInput = parseFloat(document.getElementById('sInput').value || 0);
var dInput = parseFloat(document.getElementById('dInput').value || 0);
var pInput = parseFloat(document.getElementById('pInput').value || 0);
if (isNaN(sInput) || isNaN(dInput) || isNaN(pInput)) {
alert("You entered an invalid character. Please press 'Reset' and enter a number.");
}
}
So if pInput is undefined just use 0, but if the input has value then use that value.
SIDE NOTE: white space is actually a number, +' '; // 0