Extract of union doesn't work with in operator

[FrankiePo]

🔎 Search Terms

extract union in operator

🕗 Version & Regression Information

• I tested this on 5.6.2

⏯ Playground Link

https://www.typescriptlang.org/play/?ssl=12&ssc=7&pln=12&pc=71#code/C4TwDgpgBAggNnKBeKByAhqqAfNAjLXVAY1QG4AoC0SWZNTSi4gewDsBnYKVtgMwCWAc3oBvClElR0ALigAKAJTIAfD3YcWcCADo4LIfIypFAGgoBfKB3TABHQRA5QAShFYAnACYAeGKYVlJDUANxYBLxUmXi5pBDl4RBQAWVsACx0PdDYvFgBbJSg1AAYdAFYoAH4GLDlUAiYBPgV0BCgBNnV+YWVxKSgAegGoAAUPFkgPUHwsXKcoNhZuCAAPe252KBpoVFFpOULgqDCIsigLVB15AHZisoBmRQkpXkEhAG1WuABdJUp+oZQVaQYjACBeORfdrObYsZrGSxAA

💻 Code

type All = 'a' | 'b' | 'c';

type A = 'a';

const config = {
    a: () => console.log('a'),
} satisfies Record<A, () => void>;

const all: All = Math.random() > 0.5 ? 'a' : 'b';

if (all in config) {
    // Property 'b' does not exist on type '{ a: () => void; }'.(7053)
    config[all]();
    // expected: all is typeof 'a'
}

🙁 Actual behavior

Got an error: Property 'b' does not exist on type '{ a: () => void; }'.(7053)

🙂 Expected behavior

I expected to all be a type of 'a' after in operator. Like guard will do:

function guard(a: All): a is A {
    return a in config;
}

Additional information about the issue

No response

[jcalz]

#43284 duplicate

[typescript-bot]

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