js.pattern -k 节流模式

_.throttle = function(func, wait) {
    var context, args, timeout, result;
    var previous = 0;
    var later = function() {
      previous = new Date;
      timeout = null;
      result = func.apply(context, args);
    };
    return function() {
      var now = new Date;
      var remaining = wait - (now - previous);
      context = this;
      args = arguments;
      if (remaining <= 0) {
        clearTimeout(timeout);
        timeout = null;
        previous = now;
        result = func.apply(context, args);
      } else if (!timeout) {
        timeout = setTimeout(later, remaining);
      }
      return result;
    };
  };

  _.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;
    };
  };