oxc-project/oxc · warning · OxcDiagnostic

Interfaces cannot be constructed, only classes.

Error message

Interfaces cannot be constructed, only classes.

What it means

Oxlint's port of typescript-eslint's no-misused-new. Developers sometimes write a member `new(): Foo` inside `interface Foo` believing it declares a constructor, but interfaces cannot be constructed; only classes can. The rule detects an interface member named `new` whose return type resolves to the interface's own identifier (via get_return_type_identifier at no_misused_new.rs:26-34) and flags it.

Source

Thrown at crates/oxc_linter/src/rules/typescript/no_misused_new.rs:15

use oxc_ast::{
    AstKind,
    ast::{
        ClassElement, IdentifierReference, PropertyKey, TSSignature, TSType, TSTypeAnnotation,
        TSTypeName,
    },
};
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::{GetSpan, Span};

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

fn no_misused_new_interface_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Interfaces cannot be constructed, only classes.")
        .with_help("Consider removing this method from your interface.")
        .with_label(span)
}

fn no_misused_new_class_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Class cannot have method named `new`.")
        .with_help("This method name is confusing, consider renaming the method to `constructor`")
        .with_label(span)
}

fn get_return_type_identifier<'a, 'b>(
    return_type: Option<&'b TSTypeAnnotation<'a>>,
) -> Option<&'b IdentifierReference<'a>> {
    if let Some(return_type) = return_type
        && let TSType::TSTypeReference(type_ref) = &return_type.type_annotation
        && let TSTypeName::IdentifierReference(id) = &type_ref.type_name
    {
        Some(id)

View on GitHub (pinned to e1e7af627c)

Solutions

1. Remove the `new` member from the interface
2. Provide a class (or a separate factory function) for construction
3. If a construct signature is truly needed, have it return a different type (typically a class), not the interface itself

Example fix

// before
interface Square {
  new (size: number): Square;
  area(): number;
}

// after
class Square {
  constructor(readonly size: number) {}
  area() { return this.size ** 2; }
}

npx oxlint --deny-warnings .

When it happens

Trigger: `interface Square { new (size: number): Square; area(): number; }` - the `new` member returns the interface itself.

Common situations: Patterns copied from C# where interfaces carry constructor-ish contracts, writing DI factories, misunderstanding TS construct signatures.

Related errors

• The generic type arguments should be specified as part of th
• The generic type arguments should be specified as part of th
• Use a property signature instead of a method signature.
• Use a method signature instead of a property signature.
• an empty interface is equivalent to `{}`

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/d02e851590299494. Report an issue: GitHub.