Type of element selected from (potentially) empty array

[jaksenko]

Bug Report

🔎 Search Terms

array index element undefined

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about type of element selected from (potentially) empty array

⏯ Playground Link

Playground link with relevant code

💻 Code

const ary: string[] = [];
const firstElement = ary[0];
// `firstElement`'s type is `string` while it should be `string | undefined`
// or even better `undefined` since that can be deduced from the line above.

🙁 Actual behavior

firstElement is of type string.

🙂 Expected behavior

firstElement should be of type string | undefined or undefined if that can be deduced.

[whzx5byb]

See #39560

[jaksenko]

Thanks, I didn't know about the flag, but as soon as I turned it on I got bombarded with TS errors because the flag deals not only with arrays but also with objects. And I import a lot of objects that aren't typed until I cast them (json, css, ...).

Anyway, I still think this report is valid because TS currently doesn't follow JS specification. In JS, if index doesn't exist, it returns undefined.

[MartinJohns]

I still think this report is valid because TS currently doesn't follow JS specification.

But the problem is solved. That's exactly what the mentioned flag is for.

[jaksenko]

You are right, I guess I just don't agree with the implementation that mixes arrays with objects, but that's another story. Thank you for pointing me to the flag.

[RyanCavanaugh]

Anyway, I still think this report is valid because TS currently doesn't follow JS specification. In JS, if index doesn't exist, it returns undefined.

This is equally true of objects? Anyway.