Closed
Description
🔎 Search Terms
filter is type narrow negative
🕗 Version & Regression Information
- This starts on version 5.5
⏯ Playground Link
💻 Code
type Animal = {
breath: true,
};
type Rock = {
breath: false,
};
type Something = Animal | Rock;
function isAnimal(something: Something): something is Animal {
return something.breath
}
const test1: Something = {
breath: true,
}
const test2: Something = {
breath: false,
};
const thisIsOk = [test1, test2].filter(t => isAnimal(t));
// ^? Animal[]
const thisIsWrong = [test1, test2].filter(t => !isAnimal(t));
// ^? (Animal | Rock)[]🙁 Actual behavior
const thisIsOk = [test1, test2].filter(t => isAnimal(t));
// ^? Animal[]
const thisIsWrong = [test1, test2].filter(t => !isAnimal(t));
// ^? (Animal | Rock)[]🙂 Expected behavior
const thisIsOk = [test1, test2].filter(t => isAnimal(t));
// ^? Animal[]
const thisIsShouldBe = [test1, test2].filter(t => !isAnimal(t));
// ^? Rock[]Additional information about the issue
Filtering is working only if "positive", but if the "is" is used as a negative then it don't type narrow.