oxc-project/oxc · error · OxcDiagnostic

Do not add `then` to a class.

Error message

Do not add `then` to a class.

What it means

Raised by unicorn/no-thenable (class helper) when a class defines a `then` method, making its instances thenable. Any `await instance` or `.then()` use will assimilate it unexpectedly; the faulting input is the `then` member definition at the labeled span.

Source

Thrown at crates/oxc_linter/src/rules/unicorn/no_thenable.rs:27

use oxc_macros::declare_oxc_lint;
use oxc_span::{GetSpan, Span};

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

fn object(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Do not add `then` to an object.")
        .with_help("If an object is defined as 'thenable', once it's accidentally used in an await expression, it may cause problems")
        .with_label(span)
}

fn export(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Do not export `then`.")
        .with_help("If an object is defined as 'thenable', once it's accidentally used in an await expression, it may cause problems")
        .with_label(span)
}

fn class(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Do not add `then` to a class.")
        .with_help("If an object is defined as 'thenable', once it's accidentally used in an await expression, it may cause problems")
        .with_label(span)
}

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

declare_oxc_lint!(
    /// ### What it does
    ///
    /// Disallow defining a `then` property.
    ///
    /// ### Why is this bad?
    ///
    /// If an object is defined as "thenable", once it's accidentally
    /// used in an `await` expression, it may cause problems.
    ///
    /// ### Examples

View on GitHub (pinned to e1e7af627c)

Solutions

1. Rename the method (e.g. `thenDo`, `onFulfilled`) so instances are not thenable
2. Expose the behavior via a differently named method returning a promise

When it happens

Trigger: Thrown at crates/oxc_linter/src/rules/unicorn/no_thenable.rs:27 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/e588693642a230a3. Report an issue: GitHub.