Null narrowing doesn't work with Record and key as variable?

[undone valley]

declare const foo: Record<string, { type: any } | undefined>
const key = "red"
if (foo[key]) foo[key].type // Error: Object is possibly 'undefined'
if (foo["red"]) foo["red"].type // Works

Am I doing something wrong here? Am I supposed to use a non-null assertion or is this a bug in the type narrowing?

[brittle pawn]

you're not supposed to use a non-null assertion

and it's not a bug either

the check you performed simply doesn't carry over in that situation

and it is by design

if you check out https://www.typescriptlang.org/docs/handbook/2/narrowing.html#truthiness-narrowing

you'll see the check is performed on a variable

that way, TS knows the variable isn't falsy/nullish

but that doesn't work when accessing an attribute

since the check doesn't narrow any variable

foo can't be narrowed

neither can key

it's the combination of the 2 that is unique

[undone valley]

Hmmmm

[brittle pawn]

what you can do is assign foo[key] to a variable
can will then be narrowed by the if

[undone valley]

I should have checked in the playground... it seems this was fixed (or design changed) around TS4.7.4

[fervent lintel]

Aaron#7246

Playground Link

Preview:```ts
declare const foo: Record<
string,
{type: any} | undefined

const key = "red"
if (foo[key]) foo[key].type // Error: Object is possibly 'undefined'
if (foo["red"]) foo["red"].type // Works```

You can choose specific lines to embed by selecting them before copying the link.

[undone valley]

I'm using 4.4.3 currently... need to update!

[brittle pawn]

true

[undone valley]

To be clear, in 4.7.4 this works:

const key = "red"
if (foo[key]) foo[key].type

[brittle pawn]

righ, what I described was the old behavior

[brittle pawn]

!resolved