A convenience API for reducing code repetition in a Preact application using the FormValidityObserver.
Creates an enhanced version of the FormValidityObserver, known as the PreactFormValidityObserver. It accepts the exact same arguments as the FormValidityObserver's constructor.
An enhanced version of the FormValidityObserver, designed specifically for Preact applications. It has the same Type Parameters as the FormValidityObserver. As with the FormValidityObserver, the type of M is derived from the renderer option, and the type of R is derived from the renderByDefault option.
The following methods on the PreactFormValidityObserver are the exact same as the methods on the FormValidityObserver. These methods are bound to the observer instance to allow for safe object destructuring:
observe(form)unobserve(form)disconnect()validateFields(options)validateField(name, options)setFieldError(name, message, render)clearFieldError(name)
A utility function used to simplify the process of setting up and cleaning up a form's FormValidityObserver. Pass its return value as a ref to the form that you're validating to automate setup (i.e., the call to observe) and teardown (i.e., the call to unobserve).
The novalidate parameter indicates that the novalidate attribute should be applied to the form element when JavaScript is available to the client. By default, its value is true. (For details on why this attribute is significant, see Enabling Accessible Error Messages during Form Submissions.)
Note: If you use this
action, you should not need to callobserve,unobserve, ordisconnectdirectly.
Example
import { Component } from "preact";
import { createFormValidityObserver } from "@form-observer/preact";
// Function Components
function MyFormFunction() {
const { autoObserve } = createFormValidityObserver("focusout");
return <form ref={autoObserve()}>{/* Other Elements */}</form>;
}
// Class Components
class MyFormClass extends Component {
#observer = createFormValidityObserver("focusout");
render() {
const { autoObserve } = this.#observer;
return <form ref={autoObserve()}>{/* Other Elements */}</form>;
}
}Due to Preact's unique re-rendering model, if you're using the autoObserve utility in a component that is expected to re-render, then you might need to memoize its returned ref callback to have consistent results. In functional components, you can memoize the callback with useMemo (or useCallback). In class components, you can effectively "memoize" the callback by assigning it to the class instance during its instantiation.
import { Component } from "preact";
import { useMemo } from "preact/hooks";
import { createFormValidityObserver } from "@form-observer/preact";
function MyFormFunction() {
const { autoObserve } = useMemo(() => createFormValidityObserver("focusout"), []);
const formRef = useMemo(autoObserve, []);
// or formRef = useCallback(() => autoObserve(), []);
return <form ref={formRef}>{/* Other Elements */}</form>;
}
class MyFormClass extends Component {
#observer = createFormValidityObserver("focusout");
#formRef = this.#observer.autoObserve();
render() {
return <form ref={this.#formRef}>{/* Other Elements */}</form>;
}
}Remember that autoObserve is simply a convenience utility for calling observe and unobserve automatically. You're free to setup and teardown the FormValidityObserver manually if you prefer.
Function: configure<E>(name: string, errorMessages: PreactValidationErrors<M, E, R>): PreactFieldProps
An enhanced version of FormValidityObserver.configure for Preact. In addition to configuring a field's error messages, it generates the props that should be applied to the field based on the provided arguments.
Note: If the field is only using the configured
defaultErrorsand/or the browser's default error messages, it does not need to beconfigured.
The PreactValidationErrors<M, E, R> type is an enhanced version of the core ValidationErrors<M, E, R> type. Here is how PreactValidationErrors compares to ValidationErrors.
The following properties on the PreactValidationErrors type accept the exact same values as the corresponding properties on ValidationErrors type.
badinputvalidate
Example
import { createFormValidityObserver } from "@form-observer/preact";
function MyForm() {
const { autoObserve, configure } = createFormValidityObserver("focusout");
function validateConfirmPassword(field: HTMLInputElement): string | void {
const password = field.form?.elements.namedItem("password") as HTMLInputElement;
return field.value === password.value ? undefined : "Passwords do not match.";
}
async function validateNewUsername(field: HTMLInputElement): Promise<string | void> {
const response = await fetch("/api/username-exists", { body: field.value });
const usernameTaken = await response.text();
return usernameTaken === String(true) ? "Username is already taken" : undefined;
}
return (
<form ref={autoObserve()}>
{/* Note: Accessible <label>s and error containers were omitted from this example. */}
<input {...configure("username", { validate: validateNewUsername })} />
<input name="password" type="password" />
<input {...configure("confirm-password", { validate: validateConfirmPassword })} />
<input type="date" {...configure("date", { badinput: "Please provide a valid date." })} />
</form>
);
}All the other properties on the PreactValidationErrors type are enhancements of the corresponding properties on the ValidationErrors type, so they follow slightly different rules. For clarity, these "other properties" are:
requiredminlengthminmaxlengthmaxsteptypepattern
The rules are as follows:
1) When a constraint is configured with an ErrorDetails object, the object must include a value property specifying the value of the constraint. In this scenario, both the field's constraint value and its error message are configured.
import { createFormValidityObserver } from "@form-observer/preact";
import type { ValidatableField } from "@form-observer/preact";
function MyForm() {
const { autoObserve, configure } = createFormValidityObserver("focusout");
const requiredField = (field: ValidatableField) => `<p>${field.labels[0]?.textContent ?? "Field"} is required.</p>`;
return (
<form ref={autoObserve()}>
{/* Note: Accessible <label>s and error containers were omitted from this example. */}
<input {...configure("name", { required: { value: true, message: requiredField, render: true } })} />
<input {...configure("email", { type: { value: "email", message: "Email is invalid", render: false } })} />
<input
{...configure("comment", { maxlength: { value: 80, message: "Comment must be 80 characters or less" } })}
/>
</form>
);
}Note: A constraint can only be configured with an error message when you use the object syntax. The exception to this rule is the required constraint, which allows you to imply a value of true when you supply an error message value directly to the constraint.
import { createFormValidityObserver } from "@form-observer/preact";
import type { ValidatableField } from "@form-observer/preact";
function MyForm() {
const { autoObserve, configure } = createFormValidityObserver("focusout");
const requiredField = (field: ValidatableField) => `${field.labels[0]?.textContent ?? "Field"} is required.`;
return (
<form ref={autoObserve()}>
{/* Note: Accessible <label>s and error containers were omitted from this example. */}
<input {...configure("first-name", { required: requiredField })} />
<input {...configure("last-name", { required: "Don't ignore me..." })} />
<input {...configure("email", { required: { value: true, message: requiredField } })} />
</form>
);
}2) When a constraint is configured with a primitive value, then only the field's constraint value is configured. When the constraint is broken, the browser's default error message for that constraint will be displayed.
This syntax only exists for convenience. You are free to use the regular HTML attributes instead if you like.
import { createFormValidityObserver } from "@form-observer/preact";
import type { ValidatableField } from "@form-observer/preact";
function MyForm() {
const { autoObserve, configure } = createFormValidityObserver("focusout");
const requiredField = (field: ValidatableField) => `${field.labels[0]?.textContent ?? "Field"} is required.`;
return (
<form ref={autoObserve()}>
{/* Note: Accessible <label>s and error containers were omitted from this example. */}
<input {...configure("email-1", { required: requiredField, type: "email" })} />
<input {...configure("email-2", { required: requiredField })} type="email" />
<input name="email-3" type="email" required />
</form>
);
}The return type of configure is simply an object containing the props that should be applied to the configured field. In addition to the field's name, this object will include any validation props that were configured by the function (e.g., required, minlength, maxlength, pattern, etc.).