🔄 Node.js – Callback Pattern & Callback Functions

What is a Callback?

A callback is a function passed as an argument to another function. It allows a function to call another function and can run after another function has finished. Callback functions can also be returned as values from other functions.

This is a fundamental pattern in Node.js to handle asynchronous operations.

Compare easy understanding of callback and higher-order function:

A callback function which is executed immediately is called a synchronous callback.

Example: see the previous 'Simple Callback' example.

An asynchronous callback is used to continue or resume code execution after an asynchronous operation has completed.

Example use cases: fetching 50,000 rows from a database or reading a file with 50,000 lines. The callback function executes after the operation completes.

Node.js uses asynchronous callbacks to prevent blocking of execution.