Callbacks

Callbacks in JavaScript usually take some time getting used to. If you are coming from some other non-asynchronous programming background, you will need to understand carefully how callbacks work; you may feel like you're learning programming for the first time. As everything is asynchronous in Node, you will be using callbacks for everything without trying to carefully structure them. The most important part of the Node.js project is sometimes the code organization and module management.

Callbacks are functions that are executed asynchronously at a later time. Instead of the code reading top to bottom procedurally, asynchronous programs may execute different functions at different times based on the order and speed that earlier functions such as HTTP requests or filesystem reads happen.

Whether a function execution is sequential or asynchronous depends on the context in which it is executed:

var i=0;
function add(num){
  console.log(i);
  i=i+num;
}
add(100);
console.log(i);

If you...