Pure vs Impure Functions

Great writeup Suprabha Supi. 👍 I would also like to add that:

• Pure functions allow us to write parallel code.
• Pure functions output can also be cachable because they always return the same output, increasing code performance.
• Pure function should be composable or obey the function composition concept.

"As you all know that JavaScript is synchronous, using console or any callback or promise/fetch will make the function asynchronous."

Using console doesn't make the function asynchronous. It may likely make it technically impure though (although it doesn't affect the idempotency of the function either, so that's debatable). To be clear, a function that calls another function can still be a pure function.