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Typescript checking fails when ternary operator logic is extracted #48146
Description
Bug Report
🔎 Search Terms
- ternary operator problem
- shallow type check
- extracted ternary operator condition problem
🕗 Version & Regression Information
- V4.6.2
⏯ Playground Link
Playground link with relevant code
💻 Code
function example1(obj: { value?: number }) {
const showValue = typeof obj.value === "number";
showValue ? print(obj.value) : hide()
}
function example2(obj: { value?: number }) {
typeof obj.value === "number" ? print(obj.value) : hide()
}
function print(num: number) { console.log(num) }
function hide() { }🙁 Actual behavior
Only at example1() I'm getting this error:
Argument of type 'number | undefined' is not assignable to parameter of type 'number'.
Type 'undefined' is not assignable to type 'number'.
but the argument will never be undefined
🙂 Expected behavior
Is expected that both example1() and example2() functions compile, because, technically, they are the same
Activity
equt commentedon Mar 7, 2022
Marking the value as
readonlywill make example 1 work. And the reason has been explained in the corresponding fix PR here, which in brief is