Save Form values in ReactJS using checkboxes

Question

I created a form component using react hook forms. The component is composed from a group of checkboxes and a text input. The text input appears when user click on the last checkbox custom. The idea of this one is: when the user will click on it appears a text input and the user can add a custom answer/option. Ex: if user type test within the input then when the user will save the form, there should appear in an array test value, but custom text should't be in the array. In my application i don't have access to const onSubmit = (data) => console.log(data, "submit");, so i need to change the values within Component component. Now when i click on submit i get in the final array the custom value.
Question: how to fix the issue described above?

const ITEMS = [
  { id: "one", value: 1 },
  { id: "two", value: 2 },
  { id: "Custom Value", value: "custom" }
];

export default function App() {
  const name = "group";
  const methods = useForm();
  const onSubmit = (data) => console.log(data, "submit");

  return (
    <div className="App">
      <FormProvider {...methods}>
        <form onSubmit={methods.handleSubmit(onSubmit)}>
          <Component ITEMS={ITEMS} name={name} />
          <input type="submit" />
        </form>
      </FormProvider>
    </div>
  );
}

export const Component = ({ name, ITEMS }) => {
  const { control, getValues } = useFormContext();
  const [state, setState] = useState(false);

  const handleCheck = (val) => {
    const { [name]: ids } = getValues();

    const response = ids?.includes(val)
      ? ids?.filter((id) => id !== val)
      : [...(ids ?? []), val];

    return response;
  };

  return (
    <Controller
      name={name}
      control={control}
      render={({ field, formState }) => {
        return (
          <>
            {ITEMS.map((item, index) => {
              return (
                <>
                  <label>
                    {item.id}
                    <input
                      type="checkbox"
                      name={`${name}[${index}]`}
                      onChange={(e) => {
                        field.onChange(handleCheck(e.target.value));
                        if (index === ITEMS.length - 1) {
                          setState(e.target.checked);
                        }
                      }}
                      value={item.value}
                    />
                  </label>
                  {state && index === ITEMS.length - 1 && (
                    <input
                      {...control.register(`${name}[${index}]`)}
                      type="text"
                    />
                  )}
                </>
              );
            })}
          </>
        );
      }}
    />
  );
};

demo: https://codesandbox.io/s/winter-brook-sml0ww?file=/src/Component.js:151-1600

Answer 1

Assuming that the goal is to keep all the selections in the same group field, which must be an array that logs the selected values in provided order, with the custom input value as the last item if specified, perhaps ideally it would be easier to calculate the values in onSubmit before submitting.

But since the preference is not to add logic in onSubmit, maybe an alternative option could be hosting a local state, run the needed calculations when it changes, and call setValue manually to sync the calculated value to the group field.

Forked demo with modification: codesandbox

import "./styles.css";
import { Controller, useFormContext } from "react-hook-form";
import React, { useState, useEffect } from "react";

export const Component = ({ name, ITEMS }) => {
  const { control, setValue } = useFormContext();
  const [state, setState] = useState({});

  useEffect(() => {
    const { custom, ...items } = state;
    const newItems = Object.entries(items).filter((item) => !!item[1]);
    newItems.sort((a, b) => a[0] - b[0]);
    const newValues = newItems.map((item) => item[1]);
    if (custom) {
      setValue(name, [...newValues, custom]);
      return;
    }
    setValue(name, [...newValues]);
  }, [name, state, setValue]);

  const handleCheck = (val, idx) => {
    setState((prev) =>
      prev[idx] ? { ...prev, [idx]: null } : { ...prev, [idx]: val }
    );
  };

  const handleCheckCustom = (checked) =>
    setState((prev) =>
      checked ? { ...prev, custom: "" } : { ...prev, custom: null }
    );

  const handleInputChange = (e) => {
    setState((prev) => ({ ...prev, custom: e.target.value }));
  };

  return (
    <Controller
      name={name}
      control={control}
      render={({ field, formState }) => {
        return (
          <>
            {ITEMS.map((item, index) => {
              const isCustomField = index === ITEMS.length - 1;
              return (
                <React.Fragment key={index}>
                  <label>
                    {item.id}
                    <input
                      type="checkbox"
                      name={name}
                      onChange={(e) =>
                        isCustomField
                          ? handleCheckCustom(e.target.checked)
                          : handleCheck(e.target.value, index)
                      }
                      value={item.value}
                    />
                  </label>
                  {typeof state["custom"] === "string" && isCustomField && (
                    <input onChange={handleInputChange} type="text" />
                  )}
                </React.Fragment>
              );
            })}
          </>
        );
      }}
    />
  );
};