Performance of React Hook Form

Performance is one of the primary reasons why this library was created. React Hook Form relies on an uncontrolled form, which is the reason why the register function captures ref and the 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 an 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 easily build an accessible custom form.

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 want to do this, you can 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 simply 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. It 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 an 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 { 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>
  );
}import React, { useRef } from "react";
import { useForm } from "react-hook-form";

type Inputs = {
  firstName: string,
  lastName: string,
};

export default function App() {
  const { register, handleSubmit } = useForm<Inputs>();
  const firstNameRef = useRef<HTMLInputElement | null>(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?

Make sure you are not using value. The correct property is defaultValue.

React Hook Form is focusing on uncontrolled inputs, which means you don't need to change the input value via state via onChange. In fact, you don't need value at all. 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 these 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 possible. Additionallly, 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 why React wouldn't recognize that the actual input 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 that React Hook Form embraces native form behavior by storing input state inside each input (except custom register at useEffect). A common misconception is that input state remains with mounted or unmounted inputs. Such as when working with a modal or tab forms. Instead, the correct solution is 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 { 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>
  );
}