oxc-project/oxc · warning

Unexpected empty function

Error message

Unexpected empty function

What it means

This diagnostic comes from the same `no_empty_function` rule. When the empty function has no printable name, the rule falls back to the plain message `Unexpected empty function`. Everything else matches the named case: an empty body and the same `allow` list in the config. Anonymous functions passed as arguments are the usual source.

Source

Thrown at crates/oxc_linter/src/rules/eslint/no_empty_function.rs:30

use oxc_macros::declare_oxc_lint;
use oxc_span::Span;
use schemars::JsonSchema;
use serde::Deserialize;

use crate::{
    AstNode,
    context::LintContext,
    rule::{DefaultRuleConfig, Rule},
};

fn no_empty_function_diagnostic<S: AsRef<str>>(
    span: Span,
    fn_kind: &str,
    fn_name: Option<S>,
) -> OxcDiagnostic {
    let message = match fn_name {
        Some(name) => Cow::Owned(format!("Unexpected empty {fn_kind} `{}`", name.as_ref())),
        None => Cow::Borrowed("Unexpected empty function"),
    };
    OxcDiagnostic::warn(message)
        .with_help(format!("Consider removing this {fn_kind} or adding logic to it."))
        .with_label(span)
}

#[derive(Debug, Default, Clone)]
pub struct NoEmptyFunction {
    allow: Allowed,
}

impl From<NoEmptyFunctionConfig> for NoEmptyFunction {
    fn from(config: NoEmptyFunctionConfig) -> Self {
        let mut flags = Allowed::None;
        for kind in &config.allow {
            flags |= Allowed::from(*kind);
        }
        Self { allow: flags }

View on GitHub (pinned to e1e7af627c)

Solutions

1. Remove the call when the empty callback has no effect, or give the callback a body.
2. Pass one named `noop` utility from a shared module and allow that pattern in the config.
3. Allow anonymous kinds with the `allow` option when stubs are common in the codebase.

Example fix

// before
subscribe('tick', function () {});

// after
subscribe('tick', () => {
  logger.debug('tick');
});

// find anonymous empty functions before lint
if (/function\s*\([^)]*\)\s*{\s*}/.test(src)) throw new Error('anonymous empty function found');

When it happens

Trigger: An anonymous empty function expression in argument position: `subscribe('tick', function () {});` or `setTimeout(function () {}, 100)`. The name lookup returns `None`, so the fallback message is used.

Common situations: Callback stubs passed to map, filter, or event APIs. A third-party API requires a callback but the code has no use for it. Prototypes with arrow stubs left in place.

Related errors

• Unexpected empty {fn_kind} `{}`
• The function binding is unnecessary.
• `debugger` statement is not allowed
• Variables should not be deleted
• A regular expression literal can be confused with '/='.

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/5c3537e4eb37b638. Report an issue: GitHub.