@typescript-eslint/non-nullable-type-assertion-style

If name is a string | undefined, then name as string and name! do the same thing. The ! is shorter, and it says exactly what you're claiming, which is that the value is there. It also doesn't repeat the type, so there's nothing to update when the type changes.

--fix rewrites the assertion to !.

Configure

Off by default. This rule needs types, so turning it on makes bun lint type check your code first.

[lint.rules]
"@typescript-eslint/non-nullable-type-assertion-style" = "error" # or "warn"

Examples

Reported:

function nameOf(names: Map<string, string>, id: string) {
  return names.get(id) as string;
}

Not reported:

function nameOf(names: Map<string, string>, id: string) {
  return names.get(id)!;
}

An assertion that does more than remove null and undefined can't be written with !, so it's allowed:

function toText(value: string | number | null) {
  return value as string;
}

When not to use it

@typescript-eslint/no-non-null-assertion reports every !. Don't turn on both.