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useFieldArray

React hooks for Field Array

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

NameTypeRequiredDescription
namestring✓

Name of the field. Important: make sure name is in object shape: name=test.0.name as we don't support flat arrays.

controlObjectcontrol object is from invoking useForm. it's optional if you are using FormContext.
keyNamestring = 'id'field array key value, default to "id", you can change the key name.
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.

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

NameTypeDescription
fieldsobject & { 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; }) => voidPrepend 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; }) => voidInsert input/inputs at particular position and focus.
swap(from: number, to: number) => voidSwap input/inputs position.
move(from: number, to: number) => voidMove input/inputs to another position.
remove(index?: number | number[]) => voidRemove 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>
  );
}
CodeSandbox 
import React from 'react';
import { useForm, useWatch, useFieldArray, Control } from 'react-hook-form';

const ConditionField = ({
  control,
  index,
  register,
}: {
  control: Control;
  index: number;
}) => {
  const output = useWatch<any>({
    name: 'data',
    control,
    defaultValue: 'yay! I am watching you :)',
  });

  return (
    <>
      {output[index]?.name === "bill" && (
        <input {...register(`data[${index}].conditional`)} />
      )}
      <input
        {...register(`data[${index}].easyConditional`)}
        style={{ display: output[index]?.name === "bill" ? "block" : "none" }}
      />
    </>
  );
};

const UseFieldArrayUnregister: React.FC = () => {
  type FormValues = {
    data: { name: string }[];
  };

  const { control, handleSubmit, register } = useForm<FormValues>({
    defaultValues: {
      data: [{ name: 'test' }, { name: 'test1' }, { name: 'test2' }],
    },
    mode: 'onSubmit',
    shouldUnregister: false,
  });
  const { fields } = useFieldArray({
    control,
    name: 'data',
  });
  const onSubmit = (data: FormValues) => console.log(data);

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      {fields.map((data, index) => (
        <>
          <input
            defaultValue={data.name}
            {...register(`data[${index}].name`)}
          />
          <ConditionField control={control} register={register} index={index} />
        </>
      ))}
      <input type="submit" />
    </form>
  );
};

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>
  );
}
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