//函数调用

$("#code").typewriter();

//具体函数实现

(function($) {
   $.fn.typewriter = function() {
      this.each(function() {
         var $ele = $(this), str = $ele.html(), progress = 0;
         $ele.html('');
         var timer = setInterval(function() {
            var current = str.substr(progress, 1);
            if (current == '<') {
               progress = str.indexOf('>', progress) + 1;
            } else {
               progress++;
            }
            $ele.html(str.substring(0, progress) + (progress & 1 ? '_' : ''));
            if (progress >= str.length) {
               clearInterval(timer);
            }
         }, 75);
      });
      return this;
   };
})(jQuery);