I think the easiest way to do it is to make your function return true, so that after the function is complete, the anchor tag will behave like it normally does. This way you can also use the target-attribute if you want to use new window:

function myFunction() {

  alert(hello);

  return true;

}

<a href='http://www.google.com' onclick=myFunction(); target=google>Click me</a>