reflex-dev/reflex · error · TypeError

`children` in `{fn_name}` cannot be an `rx.EventHandler`; us

Error message

`children` in `{fn_name}` cannot be an `rx.EventHandler`; use `rx.Var[rx.Component]`.

What it means

In a component-returning `@rx.memo`, the reserved `children` slot was annotated as `rx.EventHandler`. The children slot must be `rx.Var[rx.Component]` because it receives rendered child elements, not an event callback. Reflex raises this TypeError at decoration time during event-trigger validation.

Source

Thrown at packages/reflex-base/src/reflex_base/components/memo.py:961

        msg = f"`children` in `{fn_name}` cannot be `rx.RestProp`."
        raise TypeError(msg)


def _validate_event_trigger(
    parameter: inspect.Parameter, fn_name: str, for_component: bool
) -> None:
    if not for_component:
        msg = (
            f"`rx.EventHandler` parameters are only supported on component-"
            f"returning memos. Got `{parameter.name}` in `{fn_name}`."
        )
        raise TypeError(msg)
    if parameter.name == "children":
        msg = (
            f"`children` in `{fn_name}` cannot be an `rx.EventHandler`; "
            "use `rx.Var[rx.Component]`."
        )
        raise TypeError(msg)
    if parameter.default is not inspect.Parameter.empty:
        msg = (
            f"`rx.EventHandler` parameter `{parameter.name}` in `{fn_name}` "
            "must not have a default value."
        )
        raise TypeError(msg)


def _placeholder_name_value(name: str, js_prop_name: str, for_component: bool) -> str:
    return js_prop_name + CAMEL_CASE_MEMO_MARKER if for_component else name


def _placeholder_name_passthrough(
    name: str, js_prop_name: str, for_component: bool
) -> str:
    return name

View on GitHub (pinned to 45b8ed5ab7)

Solutions

1. Annotate `children` as `rx.Var[rx.Component]`
2. If a callback is needed, add a separately named `rx.EventHandler` parameter (e.g. `on_click: rx.EventHandler`)

Example fix

// before
@rx.memo
def dialog(children: rx.EventHandler) -> rx.Component:
    ...

// after
@rx.memo
def dialog(children: rx.Var[rx.Component], on_close: rx.EventHandler) -> rx.Component:
    ...

import inspect, typing, reflex as rx

def check_children_annotation(fn) -> None:
    hints = typing.get_type_hints(fn)
    if hints.get("children") is rx.EventHandler:
        raise TypeError("children must be rx.Var[rx.Component], not rx.EventHandler")

import typing, reflex as rx

def children_slot_ok(fn) -> bool:
    hints = typing.get_type_hints(fn)
    ch = hints.get("children")
    return ch is None or (typing.get_origin(ch) is rx.Var and rx.Component in typing.get_args(ch))

When it happens

Trigger: Declaring `def my_memo(children: rx.EventHandler) -> rx.Component` — the parameter is named `children` but annotated `rx.EventHandler` instead of `rx.Var[rx.Component]`.

Common situations: Confusing the children slot with an event trigger; wanting a callback when children render and reaching for the wrong annotation; auto-generated signatures that annotate every callable prop as EventHandler.

Related errors

• `rx.Var[rx.Component]` parameters in `{fn_name}` must be nam
• `children` in `{fn_name}` cannot be `rx.RestProp`.
• `rx.EventHandler` parameters are only supported on component
• `rx.EventHandler` parameter `{parameter.name}` in `{fn_name}
• `children` in `{fn.__name__}` must be annotated as `rx.Var[r

AI-assisted analysis of reflex-dev/reflex@45b8ed5ab7 (2026-08-28). Data as JSON: /api/errors/51df1534235a7bcb. Report an issue: GitHub.