Calculated values

Two Logic properties produce values instead of true/false.

Expression

Expression continuously calculates the element's value. Whenever a referenced field changes, the result is recomputed and written into the field.

{price} * {quantity}                            line total
{firstName} + " " + {lastName}                  full name
{isCompany} ? {companyCode} : {personalCode}    pick one of two codes
sumInArray({orderLines}, "total")               sum over table rows

Rules of thumb:

• A field with an Expression is effectively computed, so combine it with Read only and users won't fight the recalculation.
• Never reference the field itself; self-referencing expressions are skipped with a console warning.
• On Number elements the result respects the element's formatting settings (fraction digits, locale).
• If the expression errors or returns nothing, the value is cleared.
• To land the result somewhere else instead of in this field, write it: {variable1} = sumInArray({orderLines}, "total"). See Writing values back.

Default value

Default value sets the initial value once, on load. The user can overwrite it.

Three forms:

Form	Example	Result
Static text	Draft	literal "Draft"
Token	{__variables.route.id}	resolved at load
Expression (prefix =)	=today()	evaluated at load

Common defaults:

=today()                        today's date
{__external.userName}           current user from the host app
{__variables.route.clientId}    id from the URL
"LT"                            fixed country pre-selection

Expression vs. Default value

	Expression	Default value
When it runs	continuously	once at load
User can override	no (recalculated)	yes
Use for	totals, derived fields	sensible starting values

Worked example: invoice line

Element	Type	Setup
quantity	Number	Default value 1
unitPrice	Number	filled from a product data source
discount	Number	Default value 0
lineTotal	Number, read-only	Expression: {quantity} * {unitPrice} * (1 - {discount} / 100)