Function isNonEmptyString

isNonEmptyString<S extends string | null | undefined>(
s: S,
): s is RelaxedExclude<NonNullable<S>, "">
Type guard that checks if a value is a non-empty string.

This function performs both a type check (ensuring the value is a string) and a length check (ensuring the string is not empty). It acts as a type guard that narrows the input type to exclude null, undefined, and empty strings.

Type Narrowing Behavior:
- Eliminates null and undefined from the type
- Excludes empty string ("") from the type
- Preserves literal string types when possible
- Whitespace-only strings are considered non-empty
Type Parameters
- S extends string | null | undefined
  The input type, which can include string, null, or undefined
Parameters
- s: S
  The value to check
Returns s is RelaxedExclude<NonNullable<S>, "">
true if s is a string with length > 0, false otherwise. When true, TypeScript narrows the type to exclude empty strings and nullish values.
Example
```
const words: readonly (string | undefined)[] = [
  'Ada',
  undefined,
  '',
  'Lovelace',
] as const;

const nonEmpty = words.filter(isNonEmptyString);

assert.deepStrictEqual(nonEmpty, ['Ada', 'Lovelace']);
```
- Defined in src/guard/is-non-empty-string.mts:38