fix: set_focus/blur_focus args stripped by get_handler_args for stateless handlers

[FarhanAliRaza]

get_handler_args() used len(args) > 1 assuming all handlers have a self parameter from a State class. Server-side events like _set_focus have no state, so their single ref parameter was incorrectly stripped, producing an empty payload and a frontend TypeError: Cannot read properties of undefined (reading ref).

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• Bug fix (non-breaking change which fixes an issue)

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[greptile-apps]

Greptile Summary

This PR fixes a bug in get_handler_args where stateless server-side event handlers (like _set_focus and _blur_focus) had their arguments incorrectly stripped. The function assumed all handlers have a self parameter by checking len(args) > 1, but stateless handlers have no self, so their single ref arg was dropped — producing an empty payload and a frontend TypeError. The fix aligns get_handler_args with the same n_self_args pattern already used in EventSpec.add_args and call_event_handler in the same file.

Confidence Score: 5/5

This PR is safe to merge — it's a minimal, well-targeted bug fix with matching unit and integration tests.

The one-line logic change is consistent with the same n_self_args pattern already applied in two other locations in the same file. No new API surface is introduced, the fix is backed by a unit test that directly exercises the EventChain pipeline, and an integration test confirms the DOM-level behavior. No P0 or P1 findings.

No files require special attention.

Vulnerabilities

No security concerns identified.

Important Files Changed

Filename	Overview
packages/reflex-base/src/reflex_base/event/init.py	One-line targeted fix: replaces len(args) > 1 with len(args) > n_self_args in get_handler_args, using the same pattern already applied consistently elsewhere in the file.
tests/units/test_event.py	Adds test_focus_event_chain_preserves_args to verify the ref arg survives EventChain.create for set_focus/blur_focus, directly covering the regression path.
tests/integration/test_server_side_event.py	Adds a browser-level integration test (test_set_focus) that clicks a button calling rx.set_focus and polls for the target input becoming the active element.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["EventSpec with stateless handler\n(e.g. _set_focus, _blur_focus)"] --> B["get_handler_args(event_spec)"]
    B --> C{"handler.state is not None?"}
    C -- "Yes (State-bound handler)" --> D["n_self_args = 1"]
    C -- "No (Stateless/server-side)" --> E["n_self_args = 0"]
    D --> F{"len(args) > 1?"}
    E --> G{"len(args) > 0?"}
    F -- "True" --> H["Return event_spec.args ✅"]
    F -- "False" --> I["Return () — correctly empty"]
    G -- "True" --> J["Return event_spec.args ✅\n(ref arg preserved — BUG FIX)"]
    G -- "False" --> K["Return () — correctly empty"]

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_{Reviews (1): Last reviewed commit: "fix: set_focus/blur_focus args stripped ..." | Re-trigger Greptile}

[codspeed-hq]

Merging this PR will not alter performance

✅ 9 untouched benchmarks

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_{Comparing FarhanAliRaza:fix-set-focus-event (3829cb1) with main (1dd2d1a)}

[FarhanAliRaza]

The test is flaky, its fix is in work in this pr #6307