Using Array.prototype.filter as a null-guard?

[RonPenton]

TypeScript Version: 2.4.0

Code

function noNulls(items: (string | null)[]): string[] {
    return items.filter(x => x !== null);   // return type is still (string | null)[]
}

Expected behavior:

Return type from filter should be string[]

Actual behavior:

Return type from filter is (string | null)[].

I know I can get around this by casting the end result, ala:

function noNulls(items: (string | null)[]): string[] {
    return items.filter(x => x !== null) as string[];
}

But that just feels... bad. I'm guessing something like this is insanely complicated, but I figured I'd put this out there in case it isn't.

[jcalz]

Duplicate of #16069?

[aluanhaddad]

@jcalz yes.

@RonPenton a slightly more expressive but equally verbose workaround would be to write

function noNulls<T>(items: (T | null)[]) {
    return items.filter((x): x is T => x !== null);
}

[mhegazy]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.