Trigger Conditions
Comparable to: Middleware guards, event filters
Key Concepts
Use the concepts below when they fit the task. Not every trigger needs a condition.
- A Condition Function is a registered function that returns a boolean (
trueorfalse) - The engine calls the condition function before the handler; the handler runs only if
true - Attach a condition to any trigger type via
condition_function_idin the trigger config - The condition function receives the same event data as the handler would
- Works with all trigger types: http, queue, cron, state, stream, subscribe
Architecture
When a trigger fires, the engine first invokes the condition function with the event data. If the condition returns true, the handler executes normally. If false, the handler is skipped silently with no error or retry.
iii Primitives Used
| Primitive | Purpose |
|---|---|
registerFunction({id}, handler) (condition) | Register the condition function (returns boolean) |
registerFunction({id}, handler) (handler) | Register the handler function |
registerTrigger({type, function_id, config: {condition_function_id}}) | Bind trigger with condition gate |
Reference Implementation
See ../references/trigger-conditions.js for the full working example — a condition-gated trigger
Also available in Python: ../references/trigger-conditions.py
Also available in Rust: ../references/trigger-conditions.rs where a business rule function filters events before the handler processes them.
Common Patterns
Code using this pattern commonly includes, when relevant:
registerFunction({id: 'conditions::is-high-value'}, async (input) => input.new_value?.amount >= 1000)— condition functionregisterFunction({id: 'orders::notify-high-value'}, async (input) => {...})— handler functionregisterTrigger({type: 'state', function_id: 'orders::notify-high-value', config: {scope: 'orders', key: 'status', condition_function_id: 'conditions::is-high-value'}})— bind with condition- Condition returns
true— handler executes - Condition returns
false— handler is skipped silently - Use
conditions::prefix for condition function IDs to keep them organized
Adapting This Pattern
Use the adaptations below when they apply to the task.
- Replace the condition logic with your business rules (threshold checks, role validation, feature flags)
- Conditions work on all trigger types — use them on HTTP triggers for auth guards, on queue triggers for message filtering
- Keep condition functions lightweight and fast since they run on every trigger fire
- Combine multiple business rules in a single condition function rather than chaining conditions
- Condition functions can call
trigger()internally to check state or other functions
Pattern Boundaries
- For registering functions and triggers in general, prefer
iii-functions-and-triggers. - For state change triggers specifically, prefer
iii-state-reactions. - For invocation modes (sync/void/enqueue), prefer
iii-trigger-actions. - Stay with
iii-trigger-conditionswhen the primary problem is gating trigger execution with a condition check.
When to Use
- Use this skill when the task is primarily about
iii-trigger-conditionsin the iii engine. - Triggers when the request directly asks for this pattern or an equivalent implementation.
Boundaries
- Never use this skill as a generic fallback for unrelated tasks.
- You must not apply this skill when a more specific iii skill is a better fit.
- Always verify environment and safety constraints before applying examples from this skill.