String array type `string | undefined`

[agile girder]

I have a string array and when I attempt to get the value from it, I get type string | undefined

[glad meteor]

bnason#0

Playground Link

Preview:```ts
const arr = ["foo", "bar", "baz"]

// For me in vscode foo is of type "string | undefined"
const foo = arr[0]

// Same here
const baz = foo.length > 0 ? foo[0] : ""```

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[fathom vapor]

that would be because you have noUncheckedIndexedAccess enabled in your tsconfig

that's normal behavior

and ts doesn't narrow string/array access from length checks, it's just kinda infeasible

[agile girder]

What would be the best way to narrow that type? explicitly checking if its undefined and using a default value? Which I feel like would never be used especially if im already checking length. I could use as string i guesss

[fathom vapor]

narrow it after the access, or just non-null assert it if you're confident where it's from

if the array is fixed length you could also type it as a tuple

[agile girder]

its not fixed length, it comes from an api call

[fathom vapor]

with the length check you could non-null assert, this is a pretty reasonable situation to use it in

or just check after access like mentioned before

[agile girder]

yea okay thanks!

[rough ether]

Technically an array can have holes in it, so foo[0] is still undefined. But that's a pretty niche scenario.

[fathom vapor]

json can't encode sparse arrays, so not an issue here

[glad meteor]

sandiford#0

Playground Link

Preview:```ts
const arr = ["foo", "bar", "baz"]

delete arr[0]

// For me in vscode foo is of type "string | undefined"
const foo = arr[0]
// ^?

// Same here
const baz = arr.length > 0 ? arr[0] : ""
// ^?

console.log(arr[0])```

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[fathom vapor]

tbh you're better off pretending sparse arrays don't exist lol
you shouldn't be making them anyways

[rough ether]

yeah I think that's what most people do. Just pointing it out.