If a union has undefined an initializer will remove null or void from the union as well. #14406
Description
TypeScript Version: locally with 2.2.1 and in playground
Code
with strictNullChecks option in playground
type Opaque = {} | null | void | undefined;
class VersionOne {
x: Opaque;
constructor(x: {} | null | void = null) {
this.x = x;
}
}
new VersionOne(<Opaque>2);
class VersionTwo {
constructor(public x: {} | null | void = null) {
}
}
new VersionTwo(<Opaque>1);
class VersionThree {
constructor(public x: Opaque = null) { // null is not assignable to {}
}
}
new VersionThree(<Opaque>1); // null is not assignable to {} | undefined
class VersionFour {
constructor(public x: number | void | undefined = 1) {
}
};
let y = new VersionFour().x + 5; // should error but does not
class VersionFive {
constructor(public x: number | void = 1) {
}
};
y = new VersionFive().x + 3; // plus cannot be applied to number | voidExpected behavior:
if undefined is specified explicitly by a union the initializer should not remove the void or null along with undefined.
I would expect VersionThree to behave like VersionTwo and VersionFour to be like VersionFive
Actual behavior:
adding undefined to the type union causes the resulting type to lose null or void.