Answer to the 1st: CORS refers to cross-origin resource sharing. It's a browser mechanism that allows web pages in one domain to have controlled access to resources in other domains (cross-domain requests) 2nd: APIs (Application Programming Interfaces) are sets of rules and protocols that define how software programs or devices can communicate with each other. APIs that conform to the design principles of REST, or representational state transfer, are known as REST APIs 3rd: the event is captured and handled first by the innermost element, and then propagates to the outermost element is Event Bubbling and vice-versa is Event Capturing.