Repository navigation
TypeScript should respect "instanceof" in logical expressions #31291
Description
Hello!
Thank you for your hard work.
Please, consider this code:
class Foo {
foo: string;
}
class Bar {
bar: string;
}
function foo(value: Foo | Bar) {
const isFoo = value instanceof Foo;
const isBar = !isFoo && value.bar; // <-- causes error
}The line above throws an error:
Property 'bar' does not exist on type 'Foo | Bar'.
Property 'bar' does not exist on type 'Foo'.
However, if I replace the logical variable with the expression directly, it works:
const isBar = !(value instanceof Foo) && value.bar;
The isFoo variable in my example is a boolean constant, it's value can't change, so I believe it should be statically analyzable.
Activity
j-oliveras commentedon May 7, 2019
Typescript don't track related variables.
JakeTunaley commentedon May 8, 2019
Duplicate of #12184
typescript-bot commentedon May 11, 2019
This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.