is

• is(fn: function): this

• Test if the value matches a custom validation function. The validation function should return true if the value passes the function. If the function either returns false or a string, the function fails and the string will be used as error message.

  Parameters

  • fn: function

    Validation function.

    • • (value: boolean): boolean | string

      • Parameters

        • value: boolean

        Returns boolean | string

  Returns this