Route-based code splitting is a technique for splitting code based on the location of the component in the application. Route-based code splitting allows components to be loaded on-demand based on the user's navigation, reducing the initial load time of the application. Route-based code splitting is typically used with libraries like React Router to enable on-demand loading of code.

In React, you can use the dangerouslySetInnerHTML prop to set the inner HTML of a component. The dangerouslySetInnerHTML prop is used to bypass React's built-in sanitization and allow arbitrary HTML to be injected into a component. However, this should be used with caution, as it can pose a security risk.

JavaScript URLs are not allowed in React16.9 or any modern web development framework due to security concerns. JavaScript URLs are URLs that begin with "javascript:", and they allow for the execution of arbitrary JavaScript code when clicked. This can be used for malicious purposes, such as stealing user data or injecting malware. Instead of using JavaScript URLs, developers should use event handlers and other safe mechanisms to handle user interactions.

The "constructor" method and "getInitialState" method are both used to initialize the state of a component in React, but they are used in different class styles. The "constructor" method is used in ES6 classes, while "getInitialState" is used in ES5 classes. In general, it is recommended to use the "constructor" method in modern React code.

Pure components in React are components that implement the shouldComponentUpdate lifecycle method to improve performance. This method compares the current props and state to the next props and state, and determines whether the component needs to be re-rendered. If the props and state have not changed, the component can skip the rendering process.

When a component's state changes in React, it updates the Virtual DOM and calculates the most efficient way to update the actual DOM based on the differences between the two versions. This approach minimizes the number of changes that need to be made to the actual DOM and improves performance.

JSX prevents injection attacks by escaping special characters. When JSX is compiled, special characters are automatically escaped, preventing them from being interpreted as code. This helps to prevent XSS (cross-site scripting) attacks.

Decorators in React can be used as class decorators to add functionality to a component class. For example, you can use a decorator to add additional lifecycle methods or state to a component. Decorators can be written as higher-order components (HOCs) or as regular functions.

You can use PropTypes.oneOfType() to allow a prop to have multiple possible types. For example, you can define a prop that can be either a string or a number like this: 'myProp: PropTypes.oneOfType([PropTypes.string, PropTypes.number])'. This will allow the prop to accept values of either type, and will throw a warning if a value of a different type is passed in.

In React, you can focus an input element on page load by using the "focus()" method in the "componentDidMount()" lifecycle method. This will set the focus to the input element after the component has been mounted in the DOM. For example: componentDidMount() { this.myInput.focus(); }.