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Domain: JavaScriptHelp WantedPossible Improvement

Description

JavaScript Intellisense doesn't detect types of properties defined in async constructors

Summary

A popular asynchronous constructor pattern in JavaScript is using an async IIFE in the constructor which returns this at the end. E.g.

constructor() {
	return (async () => {
		this.#x = 42;
		this.y = 42;

		return this;
	})();
}

However, VSCode Intellisense does not infer the types for properties defined in such a constructor.

Steps to reproduce

Open a blank JavaScript, and paste in the following code:

class Class1 {
	#x;
	y;
	constructor() {
		this.#x = 42;
		this.y = 42;
	}
}
class Class2 {
	#x;
	y;
	constructor() {
		return (async () => {
			this.#x = 42;
			this.y = 42;

			return this;
		})();
	}
}

Hover over y in Class1 and observe the tooltip: (property) Class1.y: number
Hover over y in Class2 and observe the tooltip: (property) Class2.y: any

Does this issue occur when all extensions are disabled?: Yes

VS Code Version: 1.97.0
OS Version: Windows 11

Contributor guide

Tech stack: typescriptjavascript
Domain: developer experiencetooling
Issue type: bug
Difficulty: 3
Estimated time: 3-5 days
Activity status: fresh
Clarity: clear
Prerequisites: Understanding of TypeScript's type inferenceFamiliarity with class constructors and async patterns
Newbie friendliness: 45
Research direction: The issue describes a specific pattern where an async IIFE in a constructor prevents type inference for properties. To resolve, investigate the TypeScript type checker's handling of constructor return types and control flow analysis, particularly in `src/compiler/checker.ts`. Look for how property assignments inside async IIFEs are tracked. There are no linked PRs or comments yet, so the first step is to understand the relevant code paths.