Performance of React Hook Form

Performance is one of the primary reasons why this library was created. React Hook Form relies on uncontrolled form, which is the reason why the register function capture ref and controlled component has its re-rendering scope with Controller or useController. This approach reduces the amount of re-rendering that occurs due to a user typing in input or other form values changing at the root of your form or applications. Components mount to the page faster than controlled components because they have less overhead. As a reference, there is a quick comparison test that you can refer to at this repo link.

How to create an accessible input error and message?

React Hook Form is based on Uncontrolled Components, which gives you the ability to build an accessible custom form easily.

import React from "react";
import { useForm } from "react-hook-form";

export default function App() {
  const { register, handleSubmit, formState: { errors } } = useForm();
  const onSubmit = data => console.log(data);

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <label htmlFor="firstName">First name</label>
      <input
        id="firstName"
        aria-invalid={errors.firstName ? "true" : "false"}
        {...register('firstName', { required: true })}
      />
      {errors.firstName && (
        <span role="alert">
          This field is required
        </span>
      )}

      <input type="submit" />
    </form>
  );
}

Does it work with Class Components?

No, not out of the box. If you wanted to do this, you could build a wrapper around it and use it in your Class Component.

You can’t use Hooks inside of a class component, but you can definitely mix classes and function components with Hooks in a single tree. Whether a component is a class or a function that uses Hooks is an implementation detail of that component. In the longer term, we expect Hooks to be the primary way people write React components.

How to reset the form?

There are two methods to clear the form:

• HTMLFormElement.reset()

  This method does the same thing as clicking a form's reset button, and only clears input/select/checkbox values.

• React Hook Form API: reset()

  React Hook Form's reset method will reset all field values, and will also clear all errors within the form.

How to initialize form values?

Being that React Hook Form relies on uncontrolled form, you can specify a defaultValue or defaultChecked to an individual field. However, it is more common and recommended to initialize a form by passing defaultValues to useForm.

import React from "react";
import { useForm } from "react-hook-form";

export default function App() {
  const { register, handleSubmit } = useForm({
    defaultValues: {
      firstName: "bill",
      lastName: "luo",
      email: "bluebill1049@hotmail.com"
    }
  });
  const onSubmit = data => console.log(data);

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <input {...register("firstName")} />
      <input {...register("lastName")} />
      <input {...register("email")} />

      <button type="submit">Submit</button>
    </form>
  );
}

How to share ref usage?

React Hook Form needs a ref to collect the input value, however, you may want to use ref for other purposes (e.g. scroll into the view, or focus).

import React, { useRef } from "react";
import { useForm } from "react-hook-form";

export default function App() {
  const { register, handleSubmit } = useForm();
  const firstNameRef = useRef(null);
  const onSubmit = data => console.log(data);
  const { ref, ...rest } = register('firstName');

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <input {...rest} name="firstName" ref={(e) => {
        ref(e)
        firstNameRef.current = e // you can still assign to ref
      }} />

      <button>Submit</button>
    </form>
  );
}

What if you don't have access to ref?

You can actually register an input without a ref. In fact, you can manually setValue, setError and trigger.

Note: Because ref has not been registered, React Hook Form won't be able to register event listeners to the inputs. This means you will have to manually update value and error.

import React, { useEffect } from "react";
import { useForm } from "react-hook-form";

export default function App() {
  const { register, handleSubmit, setValue, setError } = useForm();
  const onSubmit = data => console.log(data);

  useEffect(() => {
    register("firstName", { required: true });
    register("lastName");
  }, []);

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <input
        name="firstName"
        onChange={e => setValue("firstName", e.target.value)}
      />
      <input
        name="lastName"
        onChange={e => {
          const value = e.target.value;
          if (value === "test") {
            setError("lastName", "notMatch")
          } else {
            setValue("lastName", e.target.value)
          }
        }}
      />
      <button>Submit</button>
    </form>
  );
}

Why is the first keystroke not working?

Double check if you are using value instead of defaultValue.

React Hook Form is focusing on uncontrolled inputs, which means you don't need to change the input value via state via onChange. This means you don't need value at all, and in fact, you only need to set defaultValue for the initial input value.

import { useForm } from 'react-hook-form/dist/index.ie11'; // V6
import { useForm } from 'react-hook-form/dist/react-hook-form.ie11'; // V5'
// Resolvers
import { yupResolver } from '@hookform/resolvers/dist/ie11/yup';

React Hook Form, Formik or Redux Form?

First of all, all libs try to solve the same problem: make the form building experience as easy as possible. However, there are some fundamental differences between the three. react-hook-form is built with uncontrolled inputs in mind and tries to provide your form with the best performance and least amount of re-renders as possible. On top of that, react-hook-form is built with React Hooks and used as a hook, which means there is no Component for you to import. Here are some of the detailed differences:

watch vs getValues vs state

Why is default value not changing correctly with ternary operator?

React Hook Form doesn't control your entire form and inputs, which is the reason why React wouldn't recognize the actual input that has been exchanged or swapped. As a solution, you can resolve this problem by giving a unique key prop to your input. You can also read more about the key props from this article written by Kent C. Dodds.

import React from "react";
import { useForm } from "react-hook-form";

export default function App() {
  const { register } = useForm();

  return (
    <div>
      {watchChecked ? (
        <input {...register("input3")} key="key1" defaultValue="1" />
      ) : (
        <input {...register("input4")} key="key2" defaultValue="2" />
      )}
    </div>
  );
}

How to work with modal or tab forms?

It's important to understand React Hook Form embraces native form behavior by storing input state inside each input (except custom register at useEffect). One of the common misconceptions is that when working with modal or tab forms, by mounting and unmounting form/inputs that inputs state will remain. That is incorrect. Instead, the correct solution would be to build a new form for your form inside each modal or tab and capture your submission data in local or global state and then do something with the combined data.

• Modal form and toggle inputs example

• Tab form example

Alternatively you can use the _deprecated_ option shouldUnregister: false when calling `useForm`.

import React from "react";
import { useForm, Controller } from "react-hook-form";

function App() {
  const { control } = useForm();
  
  return (
    <Controller
      render={({ field }) => <input {...field} />}
      name="firstName"
      control={control}
      defaultValue=""
    />
  );
}

import React, { useEffect } from "react";
import { useForm } from "react-hook-form";

function App() {
  const { register, watch, setValue, handleSubmit } = useForm({
    defaultValues: {
      firstName: "",
      lastName: ""
    }
  });
  const { firstName, lastName } = watch();

  useEffect(() => {
    register("firstName");
    register("lastName");
  }, [register]);

  const handleChange = (e, name) => {
    setValue(name, e.target.value);
  };

  const onSubmit = data => console.log(data);

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <input
        onChange={(e) => handleChange(e, "firstName")}
        value={firstName}
      />

      <input onChange={(e) => handleChange(e, "lastName")} value={lastName} />
      <input type="submit" />
    </form>
  );
}

Controller not working with shouldFocusError? (V6)

After a validation error, React Hook Form will automatically focus the invalids elements that have a proper ref, like the native inputs (eg: <input />) or some 3rd party Components that correctly export a ref (eg: from MUI <TextField inputRef={register({required: 'Field Required'})} />)

However, for some 3rd party controlled Components (like <Autocomplete> from MUI or <XX> from AntD) it's very difficult to predict its ref because the formats vary. In this case, React Hook Form will properly detect the validation error but will not be able to automatically focus that kind of Component.

As a workaround, after the validation error, you can manually focus the 3rd party controlled Component (if you can get the actual internal input ref), for example:

import React, { useEffect, useRef } from "react"
import { useForm } from "react-hook-form"

export default function App() {
  const inputRef = useRef();
  const { control, handleSubmit, formState } = useForm({});

  useEffect(() => {
    if (formState.errors.test) {
      inputRef.current.focus();
    }
  }, [formState]);

  return (
    <form onSubmit={handleSubmit(data => console.log(data))}>
      <Controller as={<ExternalInput ref={inputRef} />} name="test" control={control} rules={{ required: true }} />
      <button>Submit</button>
    </form>
  );
}

If you find difficult to make the autofocus with external controlled component work correctly, it is possible to disable the "autofocus on error" feature. It is possible that this behavior will bring a better user experience in some cases. useForm({shouldFocusError: false});