normalizeString

Normalizes a value into a trimmed string or returns null.

This helper accepts only native JavaScript strings. It trims leading and trailing whitespace but performs no other transformations. It never throws and never mutates input.

Use this when you need a predictable string before validation or further processing.

Signature

function normalizeString(value: unknown): string | null

Parameters

Name	Data type	Description
value	unknown	The value to normalize into a string.

Returns

One of:

• A trimmed string.
• null: if the value is not a native string.

Behavior

• Only native strings are accepted.
• The returned string is trimmed.
• Empty strings remain empty after trimming.
• All non-string values return null.
• No coercion (for example, converting numbers to strings) is performed.
• No Unicode normalization or case folding is applied.

Examples

normalizeString("hello")          // "hello"
normalizeString("  hello  ")      // "hello"
normalizeString("\nhello\t")      // "hello"

normalizeString("")               // ""
normalizeString("   ")            // ""

normalizeString(123)              // null
normalizeString(true)             // null
normalizeString(null)             // null
normalizeString(undefined)        // null
normalizeString({})               // null

Notes

• Empty strings are valid normalized values and are never converted to null.
• This intentional behavior distinguishes normalizeString from normalizeNonEmptyString.
• Use normalizeNonEmptyString if you need to reject empty results.
• This helper is ideal for optional or flexible string fields.
• Use validateString if you need a Result<T> instead of null.

Next up

normalizeNonEmptyString