A callback is an executable code or function that is passed as an argument to other function or code. A callback allows a lower-level software layer to call a function or subroutine defined in a higher level layer. The callback function is used by most web development services as an insurance policy for unexpected events in a program.

A web site development services programmer uses callback as an easy alternative to polymorphism and generic programming. It passes different function handlers to the lower-level software layer to dynamically determine the exact behavior of a function. This can be a powerful method for code reuse and a web development service knows this feature better than anyone else.

Web development services in India have expert programmers that use callbacks in programming languages like Java. Although Java does not support a callback function, still the experts have the tricks and techniques to force a callback function in Java.