javascript void functions

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?

void is an operator that is used to return a undefined value so the browser will not be able to load a new page. An important thing to note about the void operator is that it requires a value and cannot be used by itself.

javascript:void(0) can be considered as "Do nothing". Not sure what was intended to be achieved with it here. If you wanted to prevent form submission on button click, you should have used something like

<input type='submit' value='submit' onClick='return false;' />