validateURL

Validates that a value is a valid absolute URL string.

This helper ensures that a string value represents a fully-qualified URL with a scheme and host. It never mutates input and never throws.

Internally, it uses the isURL type guard for runtime-safe validation.

Signature

function validateURL(value: unknown): string | null

Parameters

Name	Data type	Description
value	unknown	The value to validate.

Returns

• The original string if it is a valid absolute URL.
• null: If invalid.

Behavior

• Accepts strings only.
• Requires a scheme followed by ://.
• Rejects malformed URLs that URL would otherwise normalize incorrectly.
• Never throws and never mutates input.

Examples

validateURL("http://example.com")            // "http://example.com"
validateURL("https://example.com/path")     // "https://example.com/path"
validateURL("ftp://ftp.example.com")        // "ftp://ftp.example.com"
validateURL("http:/broken.com")             // null
validateURL("justastring")                  // null
validateURL(123)                             // null

Notes

• Use when you need a predictable absolute URL before further processing or network requests
• This helper does not accept relative URLs, missing schemes, or malformed strings