debounce.js

  _.debounce = function(func, wait, immediate) {
    var timeout, result;
    return function() {
      var context = this, args = arguments;
      var later = function() {
        timeout = null;
        if (!immediate) result = func.apply(context, args);
      };
      var callNow = immediate && !timeout;
      clearTimeout(timeout);
      timeout = setTimeout(later, wait);
      if (callNow) result = func.apply(context, args);
      return result;
    };
  };