Lazy loading is a design pattern commonly used in computer programming to defer initialization of an object until the point at which it is needed.
Lazy loading is loading code only once user needs it. For Example, there is a button on the page, which shows different layout once user pressed it. So there is no need to load code for that layout on initial page load.
null is an object with no value. undefined is a type.
typeof null; // "object"
typeof undefined; // "undefined"
IIFE stands for immediately-invoked function expression; it executes immediately after created by adding a () after the function.
Your HTML code will weigh more as you use inline scripts, whereas external scripts reduces HTML file size which helps fast rendering of webpage.
CORS adds new HTTP headers that provide access to permitted origin domains. For HTTP methods other than GET (or POST with certain MIME types), the specification mandates that browsers first use an HTTP OPTIONS request header to solicit a list of supported (and available) methods from the server. The actual request can then be submitted. Servers can also notify clients whether "credentials" (including Cookies and HTTP Authentication data) should be sent with requests.
JSONP is JSON with padding.