sometimesrun.js

(function(){
  var running = false;
  var myfunction = function(){
    if(running) return;
    running = true;
    doSomethingForAWhile(function(){
      running = false;'
    });
    // OR
    for(var i = 0; i < 100000000; i++){
      doSomethingOverandOver();
    }
    running = false;
  };
  setInterval(myFunction, 100);
})();