computed-fields

Overview ¶

Computed fields — derived values the engine keeps in sync for you.

Subtotal, Tax, Total, and the checkout button's state are all DERIVED from the two inputs (Qty and UnitPrice). We never recompute them by hand in a handler: Compute() declares how each is derived and which fields it depends on, and the engine recomputes it (in dependency order) and surgically patches its bound nodes whenever a dependency changes.