void():

This operator allows inserting expressions that produce side effects
into places where an expression that evaluates to undefined is
desired.

The void operator is often used merely to obtain the undefined
primitive value, usually using void(0) (which is equivalent to void
0). In these cases, the global variable undefined can be used instead
(assuming it has not been assigned to a non-default value).
Note, however, that the javascript: pseudo protocol is discouraged over other alternatives, such as unobtrusive event handlers.

You can read more on this similar thread: What does "javascript:void(0)" mean?