IIFE is a function that runs simultaneously with the definition of a function.
It is called only the first time and cannot be called again. Using these features, it can be used where it needs to be executed only once.
A function defined within a function is called an inner function.
The Inner function child can access the variables of the parent function that contains itself. However, the parent function cannot access the variables of the inner function.
In addition, inner functions are not accessible from outside the parent function.
Recusive function is a function that calls itself.
Recursive functions have the advantage of being able to implement repetitive operations simply, but they can fall into infinite repetition and cause stackoverflow errors, so care should be taken.Escape conditions must be created to stop the call.
A callback function is a function called by the system when a specific event occurs.
The callback function is mainly used in asynchronous processing models.