oxc-project/oxc · error · OxcDiagnostic

Type assertions should be done using `toBeTypeOf`.

Error message

Type assertions should be done using `toBeTypeOf`.

What it means

Emitted by the vitest/prefer-expect-type-of rule at an expectation that asserts a type with `typeof x === 'string'` (or similar comparison) instead of vitest's `toBeTypeOf` matcher. It fires because `toBeTypeOf` is the idiomatic, more readable vitest type assertion.

Source

Thrown at crates/oxc_linter/src/rules/vitest/prefer_expect_type_of.rs:16

use oxc_ast::{
    AstKind,
    ast::{Argument, UnaryOperator},
};
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::{GetSpan, Span};

use crate::{
    context::LintContext,
    rule::Rule,
    utils::{MemberExpressionElement, PossibleJestNode, parse_expect_jest_fn_call},
};

fn prefer_expect_type_of_diagnostic(span: Span, help: &str) -> OxcDiagnostic {
    OxcDiagnostic::warn("Type assertions should be done using `toBeTypeOf`.")
        .with_help(format!("Substitute the assertion with `{help}`."))
        .with_label(span)
        .with_note("https://vitest.dev/api/expect#tobetypeof")
}

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

declare_oxc_lint!(
    /// ### What it does
    ///
    /// Enforce using [`toBeTypeOf`](https://vitest.dev/api/expect#tobetypeof) instead of `expect(typeof ...).toBe(...)`.
    ///
    /// ### Why is this bad?
    ///
    /// `expect(typeof value).toBe(type)` works but is awkward and produces poor failure messages.
    /// Vitest's built-in `toBeTypeOf` matcher performs the same `typeof` comparison with a clearer API and better error output.
    ///

View on GitHub (pinned to e1e7af627c)

Solutions

1. Replace `expect(typeof x).toBe('string')` / `expect(typeof x === 'string').toBe(true)` with `expect(x).toBeTypeOf('string')`

When it happens

Trigger: Thrown at crates/oxc_linter/src/rules/vitest/prefer_expect_type_of.rs:16 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/1f84a6ceb50f2287. Report an issue: GitHub.