reflex-dev/reflex · warning

event_chain_kwargs {event_chain_kwargs!r} are ignored for Ev

Error message

event_chain_kwargs {event_chain_kwargs!r} are ignored for EventChainVar values.

What it means

Reflex's event spec factory (EventSpec.create) emits this Python warning when you pass event_chain_kwargs (e.g. event_loader, or chain-level args like stop_propagation/prevent_default on the chain) together with an already-built EventChainVar. For literal prebuilt chains there is nowhere to attach those kwargs, so they are silently ignored and you are warned.

Source

Thrown at packages/reflex-base/src/reflex_base/event/__init__.py:894

            value: The value to create the event chain from.
            args_spec: The args_spec of the event trigger being bound.
            key: The key of the event trigger being bound.
            **event_chain_kwargs: Additional kwargs to pass to the EventChain constructor.

        Returns:
            The event chain.

        Raises:
            ValueError: If the value is not a valid event chain.
        """
        # If it's an event chain var, return it.
        if isinstance(value, Var):
            # Only pass through literal/prebuilt chains. Other EventChainVar values may be
            # FunctionVars cast with `.to(EventChain)` and still need wrapping so
            # event_chain_kwargs can compose onto the resulting chain.
            if isinstance(value, LiteralEventChainVar):
                if event_chain_kwargs:
                    warnings.warn(
                        f"event_chain_kwargs {event_chain_kwargs!r} are ignored for "
                        "EventChainVar values.",
                        stacklevel=2,
                    )
                return value
            if isinstance(value, (EventVar, FunctionVar)):
                value = [value]
            elif safe_issubclass(value._var_type, (EventChain, EventSpec)):
                return cls.create(
                    value=value.guess_type(),
                    args_spec=args_spec,
                    key=key,
                    **event_chain_kwargs,
                )
            else:
                msg = f"Invalid event chain: {value!s} of type {value._var_type}"
                raise ValueError(msg)
        elif isinstance(value, EventChain):

View on GitHub (pinned to 45b8ed5ab7)

Solutions

1. Move the kwargs into the chain construction site — build the chain with the desired options (e.g. rx.chain(..., stop_propagation=True) or pass event_loader where the EventChainVar is created) instead of at the trigger.
2. If the kwargs are redundant for this usage, delete them; the warning confirms they have no effect.
3. If you need per-trigger behavior, pass a lambda or action reference rather than a prebuilt EventChainVar, so kwargs compose onto a fresh chain.

Example fix

# before
chain = rx.action(rx.console_log('hi'))
rx.button('Go', on_click=chain, stop_propagation=True)  # warns: ignored

# after
chain = rx.action(rx.console_log('hi'), stop_propagation=True)
rx.button('Go', on_click=chain)

from reflex.vars import Var

def is_prebuilt_chain(v) -> bool:
    return isinstance(v, Var) and getattr(v, '_var_type', None).__name__ in ('EventChain',)

# only pass event_chain_kwargs when NOT passing a prebuilt EventChainVar
kwargs = {} if is_prebuilt_chain(on_click) else {'stop_propagation': True}

from reflex.event import EventChain

def is_literal_event_chain_var(v) -> bool:
    return f'{type(v).__module__}.{type(v).__name__}' == 'reflex.event.LiteralEventChainVar'

When it happens

Trigger: Calling rx.event.run_script(...)/event helpers or wiring an EventChainVar (e.g. a value already created with rx.action(...) / a LiteralEventChainVar) into an event trigger while also passing event_chain_kwargs such as {'event_loader': ...} or stopPropagation-style chain options, e.g. rx.button('Go', on_click=my_chain_var, ...custom kwargs...) via EventSpec.create / add_args / _as_event_spec.

Common situations: Migrating from passing a lambda/state action (which builds the chain lazily and accepts kwargs) to passing a prebuilt Var chain; sharing one prebuilt EventChainVar across components but trying to give each usage different chain kwargs; using .to(EventChain) casts.

Related errors

• Unexpected event type, {type(e)}.
• Invalid event chain: {value!s} of type {value._var_type}
• Invalid event: {v}
• Invalid event chain: {value}
• Unknown mime type for {image} {image_format}. Defaulting to

AI-assisted analysis of reflex-dev/reflex@45b8ed5ab7 (2026-08-28). Data as JSON: /api/errors/0980f892b0743d3d. Report an issue: GitHub.