oxc-project/oxc · error · OxcDiagnostic

Shadowing of global properties such as `undefined` is not…

Error message

Shadowing of global properties such as `undefined` is not allowed.

What it means

`no-shadow-restricted-names` reports any binding that shadows one of the five restricted names in `PRE_DEFINE_VAR`: `Infinity`, `NaN`, `arguments`, `eval`, `undefined`; with `report_global_this: true` it also reports shadowing `globalThis`. Shadowing `eval` or `arguments` is a hard SyntaxError in strict mode, and shadowing `undefined`/`NaN`/`Infinity` makes reads inside that scope silently return the local value instead of the global. The rule flags declarations, parameters, and catch bindings with these names.

Solutions

1. Rename the shadowing binding to anything else — there is no valid reason to keep these names.
2. For `globalThis` specifically, either rename the alias or disable `reportGlobalThis` in the rule config if the shim is intentional.
3. Run `oxlint --fix` is not applicable here; rename manually, then re-run the linter to confirm zero hits.

Example fix

// before
function f() {
  var undefined = false;
  return undefined; // always false, not the global undefined
}

// after
function f() {
  var isReady = false;
  return isReady;
}

# quick textual pre-check for restricted-name shadowing
rg -n '\b(var|let|const|function|class)\s+(undefined|NaN|Infinity|eval)\b|catch\s*\(\s*(undefined|NaN|Infinity|eval)\s*\)' src/

When it happens

Trigger: Writing `var undefined = 5;`, `function f(eval) {}`, `let NaN = compute();`, `catch (arguments) {}`, or (with `reportGlobalThis: true`) `const globalThis = window;`.

Common situations: Copy-pasted legacy code (pre-ES5) declaring `var undefined`; minified or machine-generated code reusing short global names; enabling `reportGlobalThis` after upgrading oxlint and hitting polyfill shims that alias `globalThis`.

Related errors

• ' ' is already a global variable.
• Variable or `function` declarations are not allowed in…
• A constructor name should not start with a lowercase letter.
• A function with a name starting with an uppercase letter…
• Accessor pair and should be grouped.

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/460ad6bcfdbc2835. Report an issue: GitHub.

Appendix: source

Thrown at crates/oxc_linter/src/rules/eslint/no_shadow_restricted_names.rs:16

use crate::{
    context::LintContext,
    rule::{DefaultRuleConfig, Rule},
};
use oxc_ast::AstKind;
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::Span;
use schemars::JsonSchema;
use serde::Deserialize;
use serde_json::Value;

const PRE_DEFINE_VAR: [&str; 5] = ["Infinity", "NaN", "arguments", "eval", "undefined"];

fn no_shadow_restricted_names_diagnostic(shadowed_name: &str, span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Shadowing of global properties such as `undefined` is not allowed.")
        .with_help(format!("Rename '{shadowed_name}' to avoid shadowing the global property."))
        .with_label(span)
}

#[derive(Debug, Default, Clone, Deserialize)]
pub struct NoShadowRestrictedNames(Box<NoShadowRestrictedNamesConfig>);

#[derive(Debug, Clone, JsonSchema, Deserialize)]
#[serde(rename_all = "camelCase", default, deny_unknown_fields)]
pub struct NoShadowRestrictedNamesConfig {
    /// If true, also report shadowing of `globalThis`.
    report_global_this: bool,
}

impl Default for NoShadowRestrictedNamesConfig {
    fn default() -> Self {
        Self { report_global_this: true }
    }

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