Retrieve value from the same page
It is possible to get the value from an element outside of the actual form. In order to do this, we need an input element with an individual selector like an ID or a class:
<input id="coffee" class="class-coffee" type="text" value="100" />
The input field’s ID is coffee, so the selector can be:
Please keep in mind that if there are multiple elements with the same selector, the plugin may not be able to retrieve the correct value. Read more about CSS selectors on MDN web docs.
Next, open up the element in the form editor, look for the option called Value_external and enter the selector there. If you want the element to listen to any changes on the target selector, set the option Value_external_listen to Yes.
Input field (#coffee)