oxc-project/oxc · warning

Prefer default export on a file with single export.

Error message

Prefer default export on a file with single export.

What it means

This is oxlint's 'import/prefer-default-export' diagnostic in its default 'single' target mode. When a module contains exactly one named export, the rule asks you to make that export the default export instead. It mirrors the ESLint rule of the same name and exists because a lone named export is usually the module's main purpose, and default import syntax makes consumers shorter and refactoring simpler.

Source

Thrown at crates/oxc_linter/src/rules/import/prefer_default_export.rs:17

use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::Span;
use schemars::JsonSchema;
use serde::{Deserialize, Serialize};
use serde_json::Value;

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

fn prefer_default_export_diagnostic(span: Span, target: Target) -> OxcDiagnostic {
    let msg = if target == Target::Single {
        "Prefer default export on a file with single export."
    } else {
        "Prefer default export to be present on every file that has export."
    };
    OxcDiagnostic::warn(msg).with_help("Prefer a default export").with_label(span)
}

#[derive(Debug, Default, PartialEq, Clone, Copy, Deserialize, Serialize, JsonSchema)]
#[serde(rename_all = "kebab-case")]
enum Target {
    /// Prefer default export when there is only one export in the module.
    #[default]
    Single,
    /// Prefer default export in any module that has exports.
    Any,
}

#[derive(Debug, Default, Clone, Deserialize, Serialize, JsonSchema)]
#[serde(rename_all = "camelCase", default, deny_unknown_fields)]
pub struct PreferDefaultExport {

View on GitHub (pinned to e1e7af627c)

Solutions

1. Convert the single named export to a default export: change 'export const x = ...' to 'const x = ...; export default x;' and update importers to 'import x from ...'.
2. If more exports are planned, add them so the file no longer has exactly one export.
3. If your style guide prefers named exports everywhere, switch the rule to target "any" is not the fix here — instead disable the rule or override it to "off" in .oxlintrc.json.
4. Suppress one-off cases with // oxlint-disable-next-line import/prefer-default-export.

Example fix

// before (theme.ts)
export const theme = { primary: 'blue' };

// after (theme.ts)
const theme = { primary: 'blue' };
export default theme;

// consumers: import theme from './theme';

// quick script: list files with exactly one non-default export
// run before enabling import/prefer-default-export
const { execSync } = require('node:child_process');
console.log(execSync("rg -l '^export (const|function|class) ' src/", { encoding: 'utf8' }));

When it happens

Trigger: Enable import/prefer-default-export with target "single" (the default) and lint a module whose module record contains exactly one export entry that is not a default export, e.g. export const theme = ... alone in a file.

Common situations: Style-guide-driven codebases (airbnb-style configs enable this rule) flag utility files, constants files, and single-component files that grew from snippets. The warning appears the moment a second export is removed during refactoring, leaving one survivor.

Related errors

• Prefer default export to be present on every file that has e
• Exporting mutable '{kind_str}' binding, use 'const' instead.
• Tried to get an allocator from an empty `FixedSizeAllocatorP
• Prefer using inline type specifiers instead of a top-level t
• Prefer using a top-level type-only import instead of inline

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/b70a1769906d2f0b. Report an issue: GitHub.