Question

Technologies:

javascript

html

reactjs

Tolerim

a month ago

How can the updated state of an object be utilized in the render of the view layer?

I am currently facing an issue with changing the state of a date value and displaying it in the view layer render. Whenever I attempt to use the value in an <h2> tag as <h2>{appointmentDate.toLocaleDateString()}</h2>, it results in the error "Cannot read properties of undefined (reading 'toLocaleDateString')". Similarly, using just "appointmentDate" as <h2>{appointmentDate}</h2> throws the error "Objects are not valid as a React child (found: [object Date]). If you meant to render a collection of children, use an array instead." I am trying to find a solution to use the updated value of "appointmentDate" outside of the function where it has been initially defined with the useState hook and modified using the "handleDate" function. I have included the relevant code below, including my unsuccessful attempt using useRef. Any suggestions would be greatly appreciated!

import { useRef, useState } from "react";
import { Calendar } from "react-date-range";
import { addDays } from "date-fns";
import { format } from "date-fns";
import "react-date-range/dist/styles.css"; 
import "react-date-range/dist/theme/default.css";

export default function App() {
  const [appointmentDate, setAppointmentDate] = useState(new Date());
  const dateRef = useRef(appointmentDate);

  const handleDate = (e) => {
    const clickedDate = e.target.value;
    setAppointmentDate(clickedDate);
    dateRef.current.innerHTML = appointmentDate.toLocaleDateString();
    console.log(appointmentDate);
  };

  return (
    <div className="App">
      <span ref={dateRef}>Select calendar</span>
      <div onClick={handleDate}>
        <Calendar
          onChange={(item) => setAppointmentDate(item)}
          date={appointmentDate}
          className="stay-date"
          name="appointmentDate"
        />
      </div>
      <h2>{appointmentDate.toLocaleDateString()}</h2>
    </div>
  );
}

(See the original code at https://codesandbox.io/s/happy-maxwell-6x28nx?file=/src/App.js:23-1034)

Answers(2)

Tolerim

a month ago

The reason why you are getting the error "Cannot read properties of undefined (reading 'toLocaleDateString')" is because you are trying to call the toLocaleDateString() on an object that is undefined. This is happening because the handleDate function is updating the state of appointmentDate asynchronously and when you try to access it outside of the function, it may not have updated yet. To solve this issue, you can use the useEffect hook to update the select-calendar element whenever the appointmentDate state changes. Here's how you can modify your code:

import { Calendar } from "react-date-range";
import { addDays } from "date-fns";
import { format } from "date-fns";
import "react-date-range/dist/styles.css"; // main css file
import "react-date-range/dist/theme/default.css"; // theme css file

export default function App() {
  const [appointmentDate, setAppointmentDate] = useState(new Date());
  const selectCalendarRef = useRef(null);

  const handleDate = (e) => {
    const clickedDate = e.target.value;
    setAppointmentDate(clickedDate);
  };

  useEffect(() => {
    if (selectCalendarRef.current) {
      selectCalendarRef.current.innerHTML = appointmentDate.toLocaleDateString();
    }
  }, [appointmentDate]);

  return (
    <div className="App">
      <span ref={selectCalendarRef}>Select calendar</span>
      <div onClick={handleDate}>
        <Calendar
          onChange={(item) => setAppointmentDate(item)}
          date={appointmentDate}
          className="stay-date"
          name="appointmentDate"
        />
      </div>
      <h2>{appointmentDate.toLocaleDateString()}</h2>
    </div>
  );
}

In this modified code, we have added a useEffect hook that updates the select-calendar element whenever the appointmentDate state changes. We are using a useRef hook to get a reference to the select-calendar element and updating its innerHTML to the current date string. We also removed the line console.log(appointmentDate) as it is not necessary for the solution and can cause performance issues.

Accepted Answer

It seems that the error message "Cannot read properties of undefined (reading 'toLocaleDateString')" is caused by the fact that the "appointmentDate" variable is undefined when the component is first rendered. One solution to this problem is to set an initial value for the "appointmentDate" variable. You can do this by changing the line where you declare the "appointmentDate" variable to:

const [appointmentDate, setAppointmentDate] = useState(new Date());

This sets the initial value of "appointmentDate" to the current date and time. Regarding your second error message "Objects are not valid as a React child (found: [object Date]). If you meant to render a collection of children, use an array instead.", it seems that you are trying to render a Date object directly in your JSX code. Instead, you should convert the Date object to a string using the "toLocaleDateString()" method before rendering it. Here's an example:

<h2>{appointmentDate.toLocaleDateString()}</h2>

This will display the date in a format that depends on the user's locale. As for your question about using the updated value of "appointmentDate" outside of the function where it has been initially defined with the useState hook and modified using the "handleDate" function, you can simply use the "appointmentDate" variable directly in your JSX code. Here's an example:

<h2>{appointmentDate.toLocaleDateString()}</h2>

This will display the updated value of "appointmentDate" whenever it changes. I hope this helps! Let me know if you have any other questions.

Sources

JavaScript Date toLocaleDateString() Method - GeeksforGeeks Cannot read property 'location' of undefined at useLocation #7015 - Github [Solved]-React Router: Cannot read property 'pathname' of undefined-Reactjs React: Uncaught TypeError: Cannot read properties of undefined React mapping ERROR: Cannot read properties of undefined (reading ...Date.prototype.toLocaleDateString() - JavaScript | MDN - Mozilla Developer