Throttle function

throttle.js

/**
 * Throttle functions.
 *
 * @param {Function} fn - The function to be throttled.
 * @param {number} delay - The delay time in milliseconds.
 * @param {Object|HTMLElement} scope - What this should be inside the function.
 * @return {Function} - The throttled function wrapped with a new function.
 */
function throttle(fn, delay, scope) {
  delay = delay || 250;
  var last;
  var defer;
  return function() {
    var scope = scope || this;
    var now = Date.now();
    var args = arguments;
    function reset() {
      clearTimeout(defer);
      defer = setTimeout(function timed() {
        last = now;
        fn.apply(scope, args);
      }, delay);
    }
    last && last + delay > now ? reset() : fn.apply(scope, args);
  }
}