Logic

Logic is a set of rules that look at the answers so far. Each rule is an expression that gives true or false, or a value. You can write the expression, or build it with the condition builder, which shows it as Field, an operator and Value.

Foldr runs every rule in the browser as the person fills in the form, and again on the server when they submit. Answers to hidden questions are dropped on the server.

The rules on a question

Open Logic & validation on a question.

Rule	Gives	Effect
Show this question when	true or false	The question is hidden until it is true.
Required when	true or false	The question must be answered while it is true.
Valid when	true or false	The answer is refused unless it is true.
Computed value (read-only)	A value	The answer is worked out and the respondent cannot change it.
Default value (editable)	A value	The answer starts as this and can be changed.

Logic and validation: the condition builder on Show this question when

{"answers": {"source": "Other", "vat_registered": true, "vat": "GB123456789"}}

Show a text box when someone picks “Other”:

answers.source == "Other"

true

Require a VAT number only for businesses that are registered:

answers.vat_registered == true

true

Check the shape of the number:

answers.vat matches /^GB[0-9]{9}$/

true

Choosing Other reveals a follow-up question

The two rules Required when and Valid when, on a VAT number question:

Required when and Valid when on the VAT number question

A Panel and Columns have a Show this panel when and a Show these columns when. Hiding one hides everything inside it.

The condition builder

Add condition picks a Field, an operator and a Value. Add group combines conditions with Match all or any of the following. Edit as expression shows the written form. A condition that the builder cannot show opens as a Custom expression.

The operators depend on the type of question: is, is not, greater than, at least, less than, at most, is empty, is answered, includes, does not include, and for dates is on, is not on, is before, is after.

Adding a condition, from Add condition to the chosen value:

Condition builder: show Please say what you supply only when What do you supply? is Other

A condition shown as an expression, with a link back to the builder:

A condition written as an expression, with a link back to the builder

Skip logic

A Page break has Skip logic. When a respondent finishes the page above, the first matching rule decides where they go: Go to a page, or Finish (submit the form), when this is true. If no rule matches, they continue to the next page. Turn off Show the page progress bar (in Settings > Look & options) when skipping makes a linear count misleading.

Skip logic on a page break: go to a page, or finish, when a condition is true

Skip logic: not VAT registered goes straight to Products

Variables

A variable is named state for the form. In Settings > Behaviour > Variables, choose Add a variable, and give it a Key, a Type (text, number or yes/no) and a Default. Read it in any rule as vars.key.

Variables let a button, or a change in one answer, show or hide parts of the form.

{"vars": {"show_extra": true}}

vars.show_extra

true

A variable key must be unique, in letters, numbers and underscores, and not start with a number.

The Variables card

Buttons and actions

A Button question runs its On click actions. A question can also run actions When this answer changes, and the form can run actions When the form opens.

Action	Does
Toggle	Flips a yes/no variable or field.
Set	Sets a field or a variable to value or to expression.
Reset	Puts a field or a variable back to blank or its default.
Run automation	Runs an approved script and puts what it returns into fields, into variables, or both. See Data sources and lookups.

When the form opens is for seeding a variable or pre-filling a field. It runs once, when someone opens the form.

The When the form opens card

A button toggles a variable and a panel appears

A Button with its On click actions:

A Button question with its On click actions

The submit button

In Settings > Behaviour > Submit button:

Setting	Does
Button text	The words on the button. The default is Submit.
Show the submit button when…	Hides the button until the expression is true. Empty means always show. Example: vars.agreed == true.
Enable the submit button when…	Greys the button until the expression is true. Empty means enable it once the required fields are filled. Example: answers.total > 0.

The Submit button card: label and when it shows or is enabled

Labels that change

Text in a label, help text or Text / HTML block can include {{ answers.key }} or {{ vars.key }}. Any expression works inside the braces.