useState is a hook in React, which is a JavaScript library for building user interfaces.

When you use useState, you are able to add state to a functional component. State is a way to store and manage information within a component.

Here's an example of how useState works:

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import React, { useState } from 'react';

function Example() {
  // The useState hook returns an array with two elements: the current state value and a function to update the state value
  const [count, setCount] = useState(0);

  // The count variable holds the current state value, and the setCount function is used to update the state value

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </div>
  );
}

In this example, the useState hook is used to add state to the Example component. The count variable holds the current state value, which is initially set to 0. The setCount function is used to update the state value. It takes a new value as an argument and updates the state with that new value.

Inside the return, the current state value (count) is displayed in a paragraph tag. When the button is clicked, the setCount function is called and the state value is incremented by 1.

Using useState allows you to create dynamic and interactive components that can update their state and rerender based on user interactions or other events.

User Interface (UI) refers to the visual and interactive components of a software application that allow the user to interact with and control the software. It includes elements like menus, buttons, icons, screens, etc. UI helps the user to interact with the software in an intuitive and easy-to-understand way. JavaScript example of UI:

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let button = document.createElement('button');
button.textContent = 'Click me!';
button.addEventListener('click', () => {
  alert('You clicked the button!');
});
document.body.appendChild(button);

A toggle button is a graphical user interface (GUI) component that allows the user to switch between two states, such as turning a feature on and off. When the button is clicked, it toggles between the two states. This component is commonly used in computer programming and software development for user input. In HTML, a toggle button can be created using the <button> element with the type="button" attribute and adding JavaScript to handle the toggling of the button. Here's an example of a toggle button in JavaScript:

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const toggleButton = document.querySelector('#toggle');

toggleButton.addEventListener('click', () => {
  toggleButton.classList.toggle('on');
});

In this example, the toggleButton variable selects the button from the HTML using querySelector(). The addEventListener() method is then used to listen for a click event on the button. When the button is clicked, the classList.toggle() method is used to add or remove the on class, which changes the appearance of the button and toggles its state.

This is quite subjective, as each technology has its own pros and cons. React is a JavaScript library for building user interfaces, while Next.js is a framework based on React. Take a look at this article for a more detailed comparison: https://blog.logrocket.com/react-vs-next-js-which-is-better/