typeof type narrowing acts differently with equivalent parentheses grouping

[ferdaber]

Bug Report

Type narrowing using the typeof operator seems to act differently if an early parenthesis grouping is used.

🔎 Search Terms

type narrowing typeof parentheses

🕗 Version & Regression Information

4.1.3

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about type narrowing

⏯ Playground Link

Playground link with relevant code

💻 Code

declare const foo: string

if (typeof foo === 'string') {
    console.log(foo)
} else {
    // @ts-expect-error
    console.log(foo.toString()) // errors, 'foo' is type 'never'
}

if ((typeof foo) === 'string') {
    console.log(foo)
} else {
    // @ts-expect-error
    console.log(foo.toString()) // doesn't error, 'foo' is still type 'string'
}

🙁 Actual behavior

In the second case, foo isn't narrowed to type never.

🙂 Expected behavior

In the second case, foo is narrowed to type never.

[RyanCavanaugh]

Narrowings only occur on predefined syntactic patterns, and this isn't one of them. I could see wanting to add parens here for clarity, though -- we should detect this one too.

[softwareCobbler]

(can I delete the above referenced commits from this thread? I put an incorrect issue reference in the commit message and it was destined for another; I do not want to pollute the repo / resolved issue list)

[RyanCavanaugh]

I don't know a way to do that. I wouldn't worry about it.

[kisfairmed]

Any chance of this to be ever fixed? It causes bigger problems in angular/angular#59215

[RyanCavanaugh]

@Andarist seems like something you might be interested to do?

[Andarist]

Expect a PR on your desk by tomorrow morning 🫡