TypeScript is misleading you about String.split

TypeScript will tell you that String.prototype.split returns a string[]. When destructuring the returned value, it will indicate that all values are strings:

const [a, b] = "test".split("/");
// a: string
// b: string

When executing the code, a is a string but b is... undefined. Run this example and look at the logs. If you were depending on b to be a string at runtime, you will run into a TypeError.

[LOG]: "string"
[LOG]: "undefined"

This was surprise number one^[1]. The second was MDN seeming to confirm that String.prototype.split returns a string[]. It does mention undefined as possible return value when using a regex separator.

Huh. Most of the "JS is weird" discourse online is overblown, but this one is truly strange. Am I missing something?