Throttle: Call a function only once every few milliseconds. Important for scroll events, or when a function is called multiple times.

throttle.js

function throttle(delay, callback) {
  var previousTime = new Date().getTime();
  return function() {
    var newTime = new Date().getTime();
    if ((newTime - previousTime) > delay) {
       previousTime = newTime;
       callback.apply(null, arguments);
    }
  };
}