Allow Boolean(val) && to refine val the same as val &&

[ghost]

Suggestion

🔍 Search Terms

boolean refinement

✅ Viability Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion

Boolean(x) && x.y should be identical to !!x && x.y as far as the type system is concerned

💻 Use Cases

use case: boolean return value along with style guides that promote Boolean(val) vs !!val

function foo(x: {y: boolean} | null): boolean {
    return !!x && x.y;
}

function foo2(x: {y: boolean} | null): boolean {
    return Boolean(x) && x.y; // error on x.y, x is possibly null
}

The one issue I could theoretically see is someone weirdly overwriting Boolean and introducing side-effects. But talk about edge cases!

I can re-write this as Boolean(x?.y), but that's not as clear IMO.

[IllusionMH]

Duplicate of #16655, #37180 and some other.
Can be found by Boolean type guard

[typescript-bot]

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