title: Uncaught TypeError: Cannot read property 'split' of undefined in jquery call back function
body: <p>I have very big trouble with <code>$.post()</code> callback. This function return some value, but when I look for its type (<code>back.type</code>) it returns "defined" and I have error loop that increase every second and it cause problems.</p>
  
  <pre><code>function upMessage() {
    var id = $(".id").val();
    var data = "id=" + id;
    $.post("ajax/upMessage.php", {
      id: id
    }, function(back) {
      back = back.split(",");
      for (var i = 0; i &lt;= (parseInt(back.length)) + 1; i++) {
        var backing = back[i];
        backing = backing.split("*");
        if (backing != "he," &amp;&amp; backing != undefined &amp;&amp; backing != "") {
          var id = backing[0];
          var oxu = backing[1];
          if (oxu == "he") {
            oxu = "&lt;i class=\"fa fa-check\" style=\"color:#2B85DB;margin-right:-7px\"&gt;&lt;/i&gt;&lt;i class=\"fa fa-check\" style=\"color:#2B85DB;\"&gt;&lt;/i&gt;";
          } else {
            oxu = "&lt;i class=\"fa fa-check\" style=\"margin-right:-7px\"&gt;&lt;/i&gt;&lt;i class=\"fa fa-check\"&gt;&lt;/i&gt;";
          }
          $("span#r" + id + ".i").html(oxu);
        }
      }
    });
  }
  setInterval(upMessage, 700);
  </code></pre>
  
  <p>I have error loop in page.
  For example.
  <a href="http://masters.az" rel="nofollow">http://masters.az</a>
  login:leo
  pass:12345</p>