In React Router v4, you can get the history object by using the "this.props.history" object passed to the component. This object contains the current history of the router, including the current location, previous locations, and navigation history. You can use this object to programmatically navigate, access the current URL, or manage the browser history.

The "componentWillReceiveProps" and "componentWillUpdate" lifecycle methods are going to be deprecated in React v16. These methods will be replaced with new lifecycle methods that are more efficient and easier to reason about. The new methods are "getDerivedStateFromProps" and "getSnapshotBeforeUpdate".

registerServiceWorker is a utility function provided by the Create React App tool that registers a new service worker with the browser. This service worker enables client-side caching of static assets and enables offline access to the application.

The create-react-class method is a way to create React class components without using ES6 syntax. This method allows components to be created using a simple object-based syntax, rather than defining a class and extending the React.Component class. The create-react-class method is useful for creating components that do not require complex logic or state management.

Higher-Order Components (HOCs) are a powerful pattern in React that allow developers to reuse code between components. HOCs can also be implemented using render props, which involves returning a new component from the higher-order component that renders the children using a function prop. This pattern is known as "render prop HOCs" and is a flexible and powerful way to share code between components.

JSX is a JavaScript syntax extension that allows developers to write HTML-like code in JavaScript. JSX is not required to use React, but it is commonly used because it makes writing and managing UI components easier.

The main goal of React Fiber is to improve client-side rendering performance. It does this by introducing a new algorithm for rendering updates that is more efficient and flexible than the previous algorithm. With React Fiber, React can break up large updates into smaller chunks, prioritize updates, and pause and resume updates as needed.

Strict mode in React is a mode that highlights potential problems in the code, such as deprecated lifecycle methods or unsafe practices. It can help identify issues early on and improve the overall quality of the code. Strict mode can be enabled globally or for individual components.

In semantic versioning (SemVer), the 'major' number represents significant changes that are not backwards-compatible. This means that if the 'major' version number increases, it indicates that there have been substantial changes in the software that may break compatibility with previous versions.

The primary purpose of implementing CORS (Cross-Origin Resource Sharing) in web development is to allow cross-origin requests. CORS is a security feature that permits or restricts web pages in one domain from making requests to a different domain, enhancing security by preventing unauthorized access to resources while enabling legitimate cross-origin communication.

In Express.js, the order in which routes are defined affects the routing mechanism. Routes are matched in the order they are defined, and the first matching route is executed. This means that the order of route definitions is crucial as it determines which route will handle a request.

JavaScript's "Object.create()" operator can be used to create a new object with the specified prototype object and properties. This method is commonly used for creating objects with specific prototypes in JavaScript, allowing for more control over inheritance and object composition.