useRef should be defined inside the component.

useRef is used to create a reference to a DOM or other element. Defining useRef outside of the component would create a single reference that would be shared among all instances of the component, which could cause unexpected behavior. By defining it inside the component, a new reference is created each time the component is rendered.

Example of using useRef in React:

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import { useRef } from 'react';

function TextInput() {
  const inputRef = useRef(null); // defining useRef inside component

  function handleClick() {
    inputRef.current.focus();
  }

  return (
    <>
      <input type="text" ref={inputRef} />
      <button onClick={handleClick}>Focus Input</button>
    </>
  );
}

In this example, useRef is defined inside the TextInput component and used to create a reference to the input element. The handleClick function references this element through the current property of the inputRef.

history.goBack() is a function in React Router that allows the user to navigate to the previous page in the browser history. If you want to define the state when using history.goBack(), you can pass the state object as a second argument to the history.push() method when navigating to the current page.

Here's an example code block in JavaScript:

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// defining state when navigating to current page
history.push('/current', { name: 'John' });

// go back to previous page
history.goBack();

In the above example, the current page is navigated to with the state object { name: 'John' }. When the history.goBack() method is called, the user will be taken to the previous page with the state from the '/current' page.

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var today = new Date();                            // Get the current date
var days = ["Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"];
var months = ["January","February","March","April","May","June","July","August","September","October","November","December"];

console.log("Today is " + days[today.getDay()] + ", " + months[today.getMonth()] + " " + today.getDate() + ", " + today.getFullYear()); 

// Output: Today is Thursday, April 4, 2020

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const date = new Date();
const year = date.getFullYear();

console.log(year);

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console.log(new Date());

This code will output the current date, for example: Tue Apr 21 2020 11:12:26 GMT+0100 (British Summer Time).

You can use the Date.now() method provided by the Javascript Date object to get the current date and time. To add this to the app, you can either create a Date instance using new Date() and assign the returned value of Date.now() to it or pass Date.now() as an argument to the function.

As an example, you can do the following in your Javascript code:

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let currentDate = new Date(Date.now());

Now currentDate will have a Date object with the value of the current date and time. You can further manipulate this Date object to adhere to the desired format for your app.

You can use the Date() object in JavaScript to retrieve the current time in any location.

Here is an example of how to use Date() to return the current time in UTC:

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const currentTime = new Date().toUTCString();
console.log(currentTime) // Returns the current time in string format