[Feature Request] store custom error message in FormControl Class

Hi, thanks for this library to make form validation easier in svelte 👍 It is possible to integrate custom error messages in the FormControl Class?

I would imagine it like this. You can define custom error messages for each validator like this:

const form = useForm({
   email: { validators: [email, required], errors: { email: "This is not a valid email address", required: "This field is required" } }
});

the FormControl Class looks like this:

"email": {
  "errors": {
   "required": "This field is required",
   "email": "This is not a valid email address"
  },
  "valid": false,
  "touched": false,
  "validators": [
   null,
   null
  ],
  "initial": "",
  "_value": ""
 },

I might be easier to define error messages in one place and can access them, via the FormControl Object

[noahsalvi]

Actually niklas@grewe is a valid email according to the specs. https://stackoverflow.com/questions/20573488/why-does-html5-form-validation-allow-emails-without-a-dot

If you want one that also requires a dot in the email you could create one like this

function email(value) {
  const emailRegex = /(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:(2(5[0-5]|[0-4][0-9])|1[0-9][0-9]|[1-9]?[0-9]))\.){3}(?:(2(5[0-5]|[0-4][0-9])|1[0-9][0-9]|[1-9]?[0-9])|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])/gm;
  if (!emailRegex.test(value)) return { email: "Email not valid"};
}

[niklasgrewe]

@noahsalvi As you mentioned, i grap the first error like this in my input.svelte component

{#if touched && errors}
   <p class="mt-2 text-sm text-yellow-600" id="email-error">{Object.values(errors)[0]}</p>
{/if}

Everhing works as i expected, but when i enter niklas@grewe i get undefined, instead of This is not a valid email address I had the same problem before in one of your REPL. I suspect that the error is due to the email validator, as it considers niklas@grewe to be a valid email address, which of course is not correct. Could you check this?