Array unions make method find into a field instead of method

[ThePrimeagen]

Bug Report

types that are unions of two types of arrays, ie string[] | number[] will make the find method go from a method to a field.

if type is just string[] or if i type it as number[] or if i type it by (string | number)[] in the example below find is a method.

🔎 Search Terms

find array method

🕗 Version & Regression Information

Started seeing it today

• Cannot compile TSC

⏯ Playground Link

TSPlayground Example

💻 Code

function wut(events: string[] | number[]) {
  events.find((e) => typeof e === "string" ? e === "foo" : e === 69);
  // --------^  find is not a method
}

🙁 Actual behavior

TSC has hurt feelings (build fails)

🙂 Expected behavior

TSC says this is great (just like map, or other array methods)

[MartinJohns]

Duplicate of #44373.

[fatcerberus]

types that are unions of two types of arrays, ie string[] | number[] will make the find method go from a method to a field.

For the record, that’s not what’s happening here at all.

Each member of the union type … has signatures, but none of those signatures are compatible with each other.

Basically, TS doesn’t know whether to use the find from string[] or the one from number[], and isn’t able to unify them because they have conflicting requirements.

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.