Overview

Conditional logic in Easy Forms is declarative. A question (or group) declares a dependents object with up to three kinds of dependency. The dependency engine subscribes to the right source fields and reacts when they change.

The three kinds

Why only three?

Earlier designs had a separate handler per behavior (visibility, options, required, read-only, min/max…). Easy Forms collapses all display and behavior changes into one kind — propsDependsOn — whose compute returns a Partial<RuntimeProps>. Adding a new dynamic prop requires zero new handler code. Value changes are the other category, split into derive (valueDependsOn) and reset (resetDependsOn).

interface BuiltInDependencies<TFormData> {
	propsDependsOn?: PropsDependencyRule<TFormData>[];
	valueDependsOn?: ValueDependency<TFormData>;
	resetDependsOn?: ResetDependency<TFormData>;
}

Typed sources

Each rule lists its fieldNames; the compute/when function receives a Pick<> of just those fields, fully typed:

dependents: {
	propsDependsOn: [{
		fieldNames: ['country'],
		compute: (v) => ({ disabled: !v.country }), // v is { country: ... }
	}],
}

Groups can declare dependencies too — see Conditional groups.