Need javascript to checkbox in PDF form based upon value not null in another text field

"If a checkbox is unchecked, it doesn't get sent, so setting it's value to 0 if it isn't checked isn't going to help - it will always return NULL."

If a checkbox or a group of radio-buttons is not checked the returned value is "Off".

"null" means that the targeted form field does not exist.

"However, it does not automatically check the boxes when the "textfield" is auto-populated with a data function from the datadase that pre-populates the text field."

In this case you should place the script as a "Validation" script instead of a "Calculation" script.

To loosely check if the variable is null, use a double equality operator(==). The double equality operator can not tell the difference between null and undefined, so it counts as same. So if you want to strict check, then don't use a double equality operator. It will lead to misconclusion.

The best way to check for a “null” value in JavaScript is to do a strict equality comparison of the value against the null keyword or Object.is() method and pass both values.

To check null in JavaScript, use triple equals operator(===) or Object.is() method. To find the difference between null and undefined, use the triple equality operator or Object.is() method.

If a checkbox is unchecked, it doesn't get sent, so setting it's value to 0 if it isn't checked isn't going to help - it will always return NULL.

There are two ways to fix this easily:

1) Assume a NULL in the PHP params means the checkbox is unchecked. If the checkbox doesn't always exist on the page, this could be problematic. By the sounds of it, there is a variable number of checkboxes, so this probably won't work.

2) Add a hidden input that has the same name as the checkbox with the value of 0 BEFORE the checkbox. If the checkbox is unchecked, the hidden field value will be used, if it is checked the checkbox value will be used.