useFieldArray

useFieldArray:
({ control?: Control, name: string, keyName?: string = 'id' }) => object

Custom hook for working with uncontrolled Field Arrays (dynamic inputs). The motivation is to provide better user experience and form performance. You can watch this short video to compare controlled vs uncontrolled Field Array.

Props

Name	Type	Required	Description
`name`	`string`	✓	Name of the field. Important: make sure name is in object shape: `name=test.0.name` as we don't support flat arrays.
`control`	`Object`		`control` object provided by `useForm`. It's optional if you are using FormContext.
`keyName`	`string = 'id'`		field array `key` value, default to "id", you can change the key name.
`shouldUnregister`	`boolean = false`		Field Array will be unregistered after unmount.

function Test() {
  const { control, register } = useForm();
  const { fields, append, prepend, remove, swap, move, insert } = useFieldArray({
    control, // control props comes from useForm (optional: if you are using FormContext)
    name: "test", // unique name for your Field Array
    // keyName: "id", default to "id", you can change the key name
  });

  return (
    {fields.map((field, index) => (
      <input
        key={field.id} // important to include key with field's id
        {...register(`test.${index}.value`)} 
        defaultValue={field.value} // make sure to include defaultValue
      />
    ))}
  );
}

Rules

The field.id (and not index) must be added as the component key to prevent re-renders breaking the fields:

// ✅ correct:
{fields.map((field, index) => (
  <div key={field.id}>
    <input ... />
  </div>
))}
// ✅ correct:
{fields.map((field, index) => <input key={field.id} ... />)}
// ❌ incorrect:
{fields.map((field, index) => <input key={index} ... />)}

defaultValue must be set for all inputs. Supplied defaultValues in the useForm hook will prepare the fields object with default value.

You can not call actions one after another. Actions need to be triggered per render.

// ❌ The following is not correct
handleChange={() => {
  if (fields.length === 2) {
    remove(0);
  }
  append({ test: 'test' });
}}

// ✅ The following is correct and second action is triggered after next render
handleChange={() => {
  append({ test: 'test' });
}}

React.useEffect(() => {
  if (fields.length === 2) {
    remove(0);
  }
}, [fields])

Each useFieldArray is unique and has its own state update, which means you should not have multiple useFieldArray with the same name.
Each input name needs to be unique, if you need to build checkbox or radio with the same name then use it with useController or controller.
Does not support flat field array.
When you append, prepend, insert and update the field array, the obj can't be empty object rather need to supply all your input's defaultValues.
```
append(); ❌
append({}); ❌
append({ firstName: 'bill', lastName: 'luo' }); ✅
```

TypeScript

when register input name, you will have to cast them as const

<input key={field.id} {...register(`test.${index}.test` as const)} defaultValue={field.test} />

we do not support circular reference. Refer to this this Github issue for more detail.

for nested field array, you will have to cast the field array by its name.

const { fields } = useFieldArray({ name: `test.${index}.keyValue` as 'test.0.keyValue' });

Return

Name	Type	Description
`fields`	`object & { id: string }`	This `object` contains the `defaultValue` and `key` for all your inputs. It's important to assign `defaultValue` to the inputs. Important: Because each input can be uncontrolled, `id` is required with mapped components to help React to identify which items have changed, are added, or are removed. {fields.map((data, index) => <input key={data.id} defaultValue={data.value} name={`data.${index}.value`} />; );}
`append`	`(obj: object \| object[], { shouldFocus?: boolean; focusIndex?: number; focusName?: string; }) => void`	Append input/inputs to the end of your fields and focus. The input value will be registered during this action.
`prepend`	`(obj: object \| object[], { shouldFocus?: boolean; focusIndex?: number; focusName?: string; }) => void`	Prepend input/inputs to the start of your fields and focus. The input value will be registered during this action.
`insert`	`(index: number, value: object \| object[], { shouldFocus?: boolean; focusIndex?: number; focusName?: string; }) => void`	Insert input/inputs at particular position and focus.
`swap`	`(from: number, to: number) => void`	Swap input/inputs position.
`move`	`(from: number, to: number) => void`	Move input/inputs to another position.
`update`	`(index?: number, obj: object) => void`	Update input/inputs at particular position.
`remove`	`(index?: number \| number[]) => void`	Remove input/inputs at particular position, or remove all when no index provided.

CodeSandbox

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

function App() {
  const { register, control, handleSubmit, reset, trigger, setError } = useForm({
    // defaultValues: {}; you can populate the fields by this attribute 
  });
  const { fields, append, prepend, remove, swap, move, insert } = useFieldArray({
    control,
    name: "test"
  });
  
  return (
    <form onSubmit={handleSubmit(data => console.log(data))}>
      <ul>
        {fields.map((item, index) => (
          <li key={item.id}>
            <input
              {...register(`test.${index}.firstName`)}
              defaultValue={item.firstName} // make sure to set up defaultValue
            />
            <Controller
              render={({ field }) => <input {...field} />}
              name={`test.${index}.lastName`}
              control={control}
              defaultValue={item.lastName} // make sure to set up defaultValue
            />
            <button type="button" onClick={() => remove(index)}>Delete</button>
          </li>
        ))}
      </ul>
      <button
        type="button"
        onClick={() => append({ firstName: "appendBill", lastName: "appendLuo" })}
      >
        append
      </button>
      <input type="submit" />
    </form>
  );
}

import * as React from "react";
import { useForm, useFieldArray, useWatch, Control } from "react-hook-form";

type FormValues = {
  cart: {
    name: string;
    price: number;
    quantity: number;
  }[];
};

const Total = ({ control }: { control: Control<FormValues> }) => {
  const formValues = useWatch({
    name: "cart",
    control
  });
  const total = formValues.reduce(
    (acc, current) => acc + (current.price || 0) * (current.quantity || 0),
    0
  );
  return <p>Total Amount: {total}</p>;
};

export default function App() {
  const {
    register,
    control,
    handleSubmit,
    formState: { errors }
  } = useForm<FormValues>({
    defaultValues: {
      cart: [{ name: "test", quantity: 1, price: 23 }]
    },
    mode: "onBlur"
  });
  const { fields, append, remove } = useFieldArray({
    name: "cart",
    control
  });
  const onSubmit = (data: FormValues) => console.log(data);

  return (
    <div>
      <form onSubmit={handleSubmit(onSubmit)}>
        {fields.map((field, index) => {
          return (
            <div key={field.id}>
              <section className={"section"} key={field.id}>
                <input
                  placeholder="name"
                  {...register(`cart.${index}.name` as const, {
                    required: true
                  })}
                  className={errors?.cart?.[index]?.name ? "error" : ""}
                />
                <input
                  placeholder="quantity"
                  type="number"
                  {...register(`cart.${index}.quantity` as const, {
                    valueAsNumber: true,
                    required: true
                  })}
                  className={errors?.cart?.[index]?.quantity ? "error" : ""}
                />
                <input
                  placeholder="value"
                  type="number"
                  {...register(`cart.${index}.price` as const, {
                    valueAsNumber: true,
                    required: true
                  })}
                  className={errors?.cart?.[index]?.price ? "error" : ""}
                />
                <button type="button" onClick={() => remove(index)}>
                  DELETE
                </button>
              </section>
            </div>
          );
        })}

        <Total control={control} />

        <button
          type="button"
          onClick={() =>
            append({
              name: "",
              quantity: 0,
              price: 0
            })
          }
        >
          APPEND
        </button>
        <input type="submit" />
      </form>
    </div>
  );
}

Tips

Custom Register

You can also register inputs at Controller without the actual input. This makes useFieldArray quick flexible to use with complex data structure or the actual data is not stored inside an input.

CodeSandbox

import * as React from "react";
import { useForm, useFieldArray, Controller, useWatch } from "react-hook-form";

const ConditionalInput = ({ control, index, field }) => {
  const value = useWatch({
    name: "test",
    control
  });

  return (
    <Controller
      control={control}
      name={`test.${index}.firstName`}
      render={({ field }) =>
        value?.[index]?.checkbox === "on" ? <input {...field} /> : null
      }
      defaultValue={field.firstName}
    />
  );
};

function App() {
  const { handleSubmit, control, register } = useForm();
  const { fields, append, prepend } = useFieldArray({
    control,
    name: "test"
  });
  const onSubmit = (data) => console.log(data);

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      {fields.map((field, index) => (
        <section key={field.id}>
          <input
            type="checkbox"
            value="on"
            {...register(`test.${index}.checkbox`)}
            defaultChecked={field.checked}
          />
          <ConditionalInput {...{ control, index, field }} />
        </section>
      ))}

      <button
        type="button"
        onClick={() => append({ firstName: "append value" }) }
      >
        append
      </button>
      <input type="submit" />
    </form>
  );
}

Controlled Field Array

There will be cases where you want to control the entire field array, which means each onChange reflects on the fields object. You can achieve this by merge with useWatch or watch's result.

CodeSandbox

import * as React from "react";
import { useForm, useFieldArray } from "react-hook-form";

export default function App() {
  const { register, handleSubmit, control, watch } = useForm<FormValues>();
  const { fields, append } = useFieldArray({
    control,
    name: "fieldArray"
  });
  const watchFieldArray = watch("fieldArray");
  const controlledFields = fields.map((field, index) => {
    return {
      ...field,
      ...watchFieldArray[index]
    };
  });

  return (
    <form>
      {controlledFields.map((field, index) => {
        return <input {...register(`fieldArray.${index}.name` as const)} />;
      })}

      <button
        type="button"
        onClick={() =>
          append({
            name: "bill"
          })
        }
      >
        Append
      </button>
    </form>
  );
}

Conditional inputs

useFieldArray is uncontrolled by default, which meansdefaultValue is rendered during input's mounting. This is different from the controlled form, which the local state is keeping updated during user interaction's onChange. When inputs get unmounted and remounted, you want to read what's in the current form values from getValue function. For individual input, you can safely use useWatchhook to retain input value as well.

CodeSandbox

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

const Input = ({ name, control, register, index }) => {
  const value = useWatch({
    control,
    name
  });
  return <input {...register(`test.${index}.age`)} defaultValue={value} />;
};

function App() {
  const [show, setShow] = React.useState(true);
  const { register, control, getValues, handleSubmit } = useForm({
    defaultValues: {
      test: [{ firstName: "Bill", lastName: "Luo", age: "2" }]
    }
  });
  const { fields, remove } = useFieldArray({
    control,
    name: "test"
  });
  const onSubmit = (data) => console.log("data", data);

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      {show && (
        <ul>
          {fields.map((item, index) => {
            return (
              <li key={item.id}>
                <input
                  defaultValue={getValues(`test.${index}.firstName`)}
                  {...register(`test.${index}.firstName`)}
                />

                <Input
                  register={register}
                  control={control}
                  index={index}
                  name={`test.${index}.age`}
                />
              </li>
            );
          })}
        </ul>
      )}
      <section>
        <button
          type="button"
          onClick={() => {
            setShow(!show);
          }}
        >
          Hide
        </button>
      </section>

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

useFieldArray

useFieldArray:({ control?: Control, name: string, keyName?: string = 'id' }) => object

Props

Rules

TypeScript

Return

Tips

Custom Register

Controlled Field Array

Conditional inputs

useFieldArray:
({ control?: Control, name: string, keyName?: string = 'id' }) => object