BaryTech interview question

"~What is CORS?,~"~What is REST give a small demonstration??~""~Questions on REACT-DOM~""~some programming questions ~""~Optimize the code ~" "~What is multithreading and how it is used? ~" "~What is a callback in JavaScript, design one?~""~A "Design pattern" is a repeatable solution for common problems occurring in software design, What are the types of design patterns??~"