Please help explaining this to a friend

Hi, I am having a hard time explaining the concept of callback functions in DOM to a friend coming from Qt/C++ background. Any thoughts how I could make it sound more friendly sounding given his background. This was my most recent attempt: The most common host environment in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of Facade Pattern is a utility to help run multiple versions of Node. Despite the performance limitations inherent to its dynamic nature, the increasing speed of JavaScript utilities designed for the web. HTTP requests. Virtual DOM is a predictable state container for apps.