The ref argument is only available for class components in React. Function components do not have an instance, so refs cannot be attached to them. Refs can be attached to DOM elements, class components, and functional components that are created using the forwardRef() method.

In React, the "setState" method is used to update component state, and it merges the new state with the old state. The "replaceState" method is similar, but it overwrites the old state completely with the new state. However, "replaceState" is deprecated in React and should not be used. Instead, you should use the "setState" method to update state in a React component.

In Create React App, you can use HTTPS instead of HTTP by setting the "HTTPS=true" environment variable. This will start the development server with HTTPS enabled, and will allow you to test your application with SSL/TLS encryption.

In React Router v4, you can get query parameters by using the "location.search" property of the current location object. This property contains the query string of the URL, including the "?" character and the parameter keys and values. To parse the query string, you can use a library like "query-string" or "URLSearchParams". For example: const queryParams = new URLSearchParams(this.props.location.search); const foo = queryParams.get('foo');.

Stateless components, also known as functional components, are components that don't use any state. Stateless components are simpler and easier to test than stateful components, but they can't be used for more complex UI components that need to maintain state.

ReactDOMServer is a module that allows you to render React components on the server. ReactDOMServer provides several methods for rendering components, including the renderToString method and the renderToStaticMarkup method.

React lazy is a function that creates a lazy version of a component. This lazy version is loaded only when it is actually needed, such as when a user navigates to a page that requires the component. This can help improve performance by reducing the initial load time of the application.

This is a subjective question and the correct answer will vary depending on the individual's experience and preferences. There is no one "correct" answer.

Refs in React are used to create references to DOM elements. They allow developers to access and manipulate the properties and methods of DOM elements directly, without the need for additional logic or event handling. Refs are typically used when working with third-party libraries, or when manipulating the DOM directly is necessary.

To pass a number to a React component, you can simply pass the number directly as a prop. React will automatically handle the conversion of the number to a string when rendering the component. For example, you could pass a number like this: ' '. If you need to pass a number as a string, you can wrap it in quotes like any other string.