What is callback function in JavaScript?

Callback Function

A callback function is a function (It can be any function Anonymous Function, Arrow Function) passed into another function as an argument, which is then invoked inside the outer function to complete some kind of routine or action.

Synchronous – It waits for each operation to complete, after that it executes the next operation.

Asynchronous – It never waits for each operation to complete, rather it executes all operations in the first GO only.