Recalculate on input change

This guide explains how to use On change actions on an Input element to automatically trigger a recalculation whenever the user changes a value — no button required. This is ideal for live, reactive forms where the output should always reflect the current input.

Prerequisite: A Calculator ruleset with inputs a (Number) and b (Number), and a rule sum = a + b. A form with two Input elements (bound to a and b) and one Output element (bound to sum).

The basic setup — adding a Calculate button that runs the ruleset — is already covered in detail in Create a Form. If you haven't done that yet, start there.

Adding On change actions to an Input element

1. Open your form and click the First input element (bound to a) to expand it
2. Scroll down to On change actions and click +
3. Select Execute Ruleset
4. Repeat steps 1–3 for the Second input element (bound to b)
5. Save the Ruleset

When you type a value in either input field, the sum output updates immediately — without clicking a button.

Conditional recalculation with Set property

You can also use On change actions to reset a downstream field when an upstream value changes. For example, when the user changes input a, clear the value of b first:

1. Click the First input element (bound to a)
2. Under On change actions, click + → select Set global variable
3. Set Path to b
4. Set Value to 0
5. Add a second action → Execute Ruleset
6. Save the Ruleset

Now when a changes, b is reset before the ruleset recalculates. This prevents stale combinations.