A custom form Hook can centralize repeated logic for form values, input changes, validation, resetting, and submission. This becomes useful when several forms follow the same basic behavior. ### Without a Form Hook A component may repeatedly contain: ```text useState for form values handleChange validation logic errors state reset logic handleSubmit ``` A custom Hook can package that behavior. ### Basic useForm Example ```jsx import { useState } from "react"; function useForm(initialValues, validate) { const [values, setValues] = useState(initialValues); const [errors, setErrors] = useState({}); function handleChange(event) { const { name, value, type, checked } = event.target; setValues((currentValues) => ({ ...currentValues, [name]: type === "checkbox" ? checked : value })); } function reset() { setValues(initialValues); setErrors({}); } function validateForm() { const nextErrors = validate ? validate(values) : {}; setErrors(nextErrors); return Object.keys(nextErrors).length === 0; } return { values, errors, handleChange, validateForm, reset }; } ``` ### Validation Function ```jsx function validateLogin(values) { const errors = {}; if (!values.email.trim()) { errors.email = "Email is required."; } if (!values.password) { errors.password = "Password is required."; } return errors; } ``` ### Using the Form Hook ```jsx function LoginForm() { const { values, errors, handleChange, validateForm, reset } = useForm( { email: "", password: "" }, validateLogin ); async function handleSubmit(event) { event.preventDefault(); if (!validateForm()) { return; } await login(values); reset(); } return ( ); } ``` ### What Should the Hook Own? A reusable form Hook can reasonably own: ```text Field values Field changes Errors Touched fields Validation Resetting ``` The component may still own business-specific behavior such as: ```text Call login API Redirect after success Show account-specific messages ``` This keeps the Hook reusable instead of tightly coupling it to one form. ### Avoid Building a Giant Universal Hook Too Early Trying to make one Hook support every possible form feature can quickly become more complicated than the components using it. Start with the behavior that genuinely repeats. ### Interview-Ready Answer A custom form Hook extracts reusable form behavior such as field state, `handleChange`, validation, errors, and resetting. The Hook should handle generic form mechanics while business-specific actions such as login or checkout usually remain in the component or feature layer. This improves reuse without making the Hook responsible for unrelated application logic.