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Validation rules & error messages

Custom validation rules

informel uses the browser built-in form validation by default, with attributes such as required, minlength, pattern, type="email", type="url" etc...

Here is an example (try submitting the form):

On top of that, it is possible to specify custom validation rules, via the `validationHandler` property:
document.querySelector('inform-el').validationHandler = ({ values }) => {
// Returns an object {'field name': 'error message'}

Custom error message

When a field is in error, the control's validationMessage is shown by default.

For example, on Google Chrome, <input type="text" required /> will show Please fill out this field. while <input type="checkbox" required /> will show Please check this box if you want to proceed..

To customize this behavior, you can either use validationHandler as shown above, or use the following attributes on <inform-field />:

  • default-error: a fixed error message displayed whenever the field is in error (regardless of the reason).
  • For each property in the native ValidityState object, <inform-field /> accepts a corresponding kebab-case attribute to specify the error message. For example, if the field is <input type="email" required /> and you want to show different errors when the value is not set or when the value doesn't have the right format, you can use the value-missing and the type-mismatch attributes. See them in action here:

When multiple errors are specified, the order of precedence is:

  1. Error returned by validationHandler
  2. <inform-field /> ValidityState attribute
  3. <inform-field /> "default-error" attribute
  4. The element native validationMessage.

Using zod for validation

A zod schema can be specified via the zodSchema property:

document.querySelector('inform-el').zodSchema = z.object({
first_name: z.string().min(1, { message: "Firstname is required" }),
last_name: z.string().min(1, { message: "Lastname is required" }),
email: z.string().min(1, { message: "Email is required" }).email({
message: "Must be a valid email",
password: z
.min(6, { message: "Password must be atleast 6 characters" }),
terms: z.literal(true, {
errorMap: () => ({ message: "You must accept Terms and Conditions" }),

Just like other validation methods, if the form values are incompatible with the schema, errors are shown and submission is blocked.

Disabling the submit button on error

When adding the error-disable-submit attribute on <inform-el />, the submit button is automatically disabled while errors are shown: