Description

export type AbstractType<T = any> = (abstract new (...args: any[]) => T) & Function;
export type ConcreteType<T = any> = (new (...args: any[]) => T) & Function;
export type Type<T = any> = AbstractType<T> | ConcreteType<T>;

export interface AbstractAssertions {
  instance<Expects extends Type<unknown>>(
    actual: unknown,
    expects: Expects,
  ): asserts actual is InstanceType<Expects>;
}

export const assert: AbstractAssertions = {
  instance(actual, expects) {
    return actual instanceof expects;
  },
};

let x = 1 as any
assert.instance(x, Error) // Error here
assert.instance(x, Date) // Error here

Contributor guide

Tech stack

typescript

Domain

developer experience

Issue type

bug

DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.

4

Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.

over 1 week

Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.

stale

ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.

clear

Prerequisites

TypeScript type systemassertion functionsregression testing

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

15

Research direction

Investigate changes to assertion type checking between TypeScript 4.8.4 and 4.9.4 by reviewing the changelog and related compiler source code. Look for modifications in the type checker or binder that affect 'asserts' predicates. Focus on how InstanceType interacts with assertion functions. Consider creating a minimal test case to isolate the regression and identify the exact commit that introduced the behavior change.