various code style options

option1.js

var handling = false;

window.onSomeEvent = function handleEvent() {
  if(handling) return;
  handling = true;
  /* some other handler code here which eventually switches handling off again */
};

option2.js

var handling = false;

window.onSomeEvent = function handleEvent() {
   handling ? return : handling = true;
  /* some other handler code here which eventually switches handling off again */
};

option3.js

var handling = false;

window.onSomeEvent = function handleEvent() {
  if(handling) {
    return;
  }
  handling = true;
  /* some other handler code here which eventually switches handling off again */
};

option4.js

var handling = false;

window.onSomeEvent = function handleEvent() {
  if(handling) {
    return;
  } else {
    handling = true;
    /* some other handler code here which eventually switches handling off again */
  }
};

Callback stacks? Can't you just use objects?