What is a callback? Expain the pros & cons of callback in node js.

Callback is a function that is passed as an argument to another function and is executed after some event or action occurs. The function that accepts the callback is often referred to as the "parent" function, and the function that is passed in as an argument is referred to as the "callback" function.

In Node.js, callbacks are used extensively to handle asynchronous operations. For example, when reading a file or making an HTTP request, the Node.js runtime will not wait for the operation to complete before moving on to the next line of code. Instead, it will pass a callback function that will be executed when the operation is completed.

Pros of Callback in Node.js:

• They allow you to handle asynchronous operations, which makes your code non-blocking and efficient.
• They provide a clear separation of concerns, allowing you to handle the success and failure cases of an operation separately.
• They are widely used in Node.js and are supported by many built-in modules, allowing you to take advantage of pre-existing functionality.
• They are compatible with most versions of Node.js, and therefore they can run on most environments.

 Cons of Callback in Node.js:

• They can lead to callback hell, which is a situation where you have nested callbacks that are hard to read and maintain.
• They don't provide a way to cancel a callback or a way to check if a callback has been called.
• They don't support the concept of return values, and it becomes difficult to handle errors when there are multiple asynchronous operations.