oxc-project/oxc · error · OxcDiagnostic

Do not use an object literal as default for parameter `{para

Error message

Do not use an object literal as default for parameter `{param}`.

What it means

Raised by unicorn/no-object-as-default-parameter when a function parameter's default value is an object literal (e.g. `function f(a = {})`). The identifier helper names the parameter; the faulting input is the default parameter at the labeled span.

Source

Thrown at crates/oxc_linter/src/rules/unicorn/no_object_as_default_parameter.rs:12

use oxc_ast::{
    AstKind,
    ast::{BindingPattern, Expression},
};
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::Span;

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

fn identifier(span: Span, param: &str) -> OxcDiagnostic {
    OxcDiagnostic::warn(format!("Do not use an object literal as default for parameter `{param}`."))
        .with_label(span)
}

fn non_identifier(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Do not use an object literal as default").with_label(span)
}

#[derive(Debug, Default, Clone)]
pub struct NoObjectAsDefaultParameter;

declare_oxc_lint!(
    /// ### What it does
    ///
    /// Disallow the use of an object literal as a default value for a parameter.
    ///
    /// ### Why is this bad?
    ///
    /// Default parameters should not be passed to a function through an object literal. The `foo = {a: false}` parameter works fine if only used with one option. As soon as additional options are added, you risk replacing the whole `foo = {a: false, b: true}` object when passing only one option: `{a: true}`. For this reason, object destructuring should be used instead.

View on GitHub (pinned to e1e7af627c)

Solutions

1. Destructure inside the default: `function f({ a, b } = {})`
2. Default each property individually: `function f(options = {}) { const a = options.a ?? defaultA }`
3. Use `undefined` as the default and build the object in the body

When it happens

Trigger: Thrown at crates/oxc_linter/src/rules/unicorn/no_object_as_default_parameter.rs:12 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/03d425890a7c3fed. Report an issue: GitHub.