React render [object Object] when using useReducer instead of JSX

Question

So I was learning my React course today on Udemy and came across an error where the react app renders [object Object] instead of the JSX (which is supposed to be an empty input box), also, since the input box has onChange method, The input value is also unable to change. Here is the image of the application and also the code given below:-


import React, { useState, useEffect, useReducer } from "react";

import Card from "../UI/Card/Card";
import classes from "./Login.module.css";
import Button from "../UI/Button/Button";

const emailReducer = (state, action) => {
  if(action.type === 'USER_INPUT'){
    return {value: action.value, isValid: action.value.includes('@')};
  }
  if(action.type === 'INPUT_BLUR'){
    return {value: state.value, isValid: state.value.includes('@')};
  }
  return { value: '', isValid: false };
};

const Login = (props) => {
  // const [enteredEmail, setEnteredEmail] = useState("");
  // const [emailIsValid, setEmailIsValid] = useState();
  const [enteredPassword, setEnteredPassword] = useState("");
  const [passwordIsValid, setPasswordIsValid] = useState();
  const [formIsValid, setFormIsValid] = useState(false);

  const [emailState, dispatchEmail] = useReducer(emailReducer, {
    value: '',
    isValid: false
  });

  useEffect(() => {
    console.log("EFFECT RUNNING");

    return () => {
      console.log("EFFECT CLEANUP");
    };
  }, []);

  const emailChangeHandler = (event) => {
    dispatchEmail({type: 'USER_INPUT', value: event.target.value});

    setFormIsValid(
      emailState.isValid && enteredPassword.trim().length > 6
    );
  };

  const passwordChangeHandler = (event) => {
    setEnteredPassword(event.target.value);

    setFormIsValid(
      emailState.isValid && event.target.value.trim().length > 6
    );
  };

  const validateEmailHandler = () => {
    dispatchEmail({type: 'INPUT_BLUR'});
  };

  const validatePasswordHandler = () => {
    setPasswordIsValid(enteredPassword.trim().length > 6);
  };

  const submitHandler = (event) => {
    event.preventDefault();
    props.onLogin(emailState.value, enteredPassword);
  };

  return (
    <Card className={classes.login}>
      <form onSubmit={submitHandler}>
        <div
          className={`${classes.control} ${
            emailState.isValid === false ? classes.invalid : ""
          }`}
        >
          <label htmlFor="email">E-Mail</label>
          <input
            id="email"
            value={emailState}
            onChange={emailChangeHandler}
            onBlur={validateEmailHandler}
          />
        </div>
        <div
          className={`${classes.control} ${
            passwordIsValid === false ? classes.invalid : ""
          }`}
        >
          <label htmlFor="password">Password</label>
          <input
            type="password"
            id="password"
            value={enteredPassword}
            onChange={passwordChangeHandler}
            onBlur={validatePasswordHandler}
          />
        </div>
        <div className={classes.actions}>
          <Button type="submit" className={classes.btn} disabled={!formIsValid}>
            Login
          </Button>
        </div>
      </form>
    </Card>
  );
};

export default Login;

score 2 · Answer 1 · answered Oct 19 '21 at 17:33

Your emailState is an object with the following shape:

{ value: string, isValid: boolean }

So in your input field you need to use the value attribute:

          <input
            id="email"
            value={emailState.value}
            onChange={emailChangeHandler}
            onBlur={validateEmailHandler}
          />

score 0 · Answer 2 · answered Oct 19 '21 at 17:35

You are passing the entire emailState object to the input when you likely want the nested value property. You can pass emailState.value to the input's value prop, or destructure the state beforehand and pass value directly.

const [{ isValid, value }, dispatchEmail] = useReducer(emailReducer, {
  value: '',
  isValid: false
});

...

<input
  id="email"
  value={value}
  onChange={emailChangeHandler}
  onBlur={validateEmailHandler}
/>

React render [object Object] when using useReducer instead of JSX

2 Answers2