Parentheses in typeof expression break narrowing

[crisbeto]

🔎 Search Terms

• type narrowing
• typeof expression

🕗 Version & Regression Information

• This changed between versions 3.3 and 5.7
• This changed in commit or PR: unclear

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.7.2#code/DYUwLgBAbghsCuIIF4IEYBMBmCMDOEeYATgJYB2A5hAD4TnwC2ARiMQNwBQnA9DxAHUA9sQDWeTqQBmEABRgAngAcQQmbARJk2iAHIGLNroCUEAN6cIEAMZDyeIaAB0wIZVkbEEAFQQMxrgBfbj4IABEhEAJyIUgAdxFRSRlZeWVVdThEU21UfSZWYhNzSxs7B2dXd08kX38gkP4IqPpYiASxZLlFFTVoLK0dWXzDIuNTCytbe0cQFzcPAZ8-AM5g3ibI6LaOpOk5NN7MzRyhkcKTCdLpirmqxc1l+rWgA

💻 Code

let value = 123 as string | number;

// Works
if (typeof value === 'number') {
  console.log(value * 2);
}

// Does not work
if ((typeof value) === 'number') {
  console.log(value * 2);
}

// Does not work
if (typeof value === ('number')) {
  console.log(value * 2);
}

// Does not work
if ((typeof value) === ('number')) {
  console.log(value * 2);
}

🙁 Actual behavior

As soon as parentheses are added around the typeof expression or the value it's being compared against, narrowing no longer works.

🙂 Expected behavior

Narrowing shouldn't be affected by parentheses.

Additional information about the issue

No response

[MartinJohns]

Duplicate of #42203.

[typescript-bot]

This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.