Check and Validate input field when loses focus

<div>
      Email:
      <input type="text" name="email" id="txtEmail" onblur="validateForm()">
      <label id="lblError" style="color:red"></label>
  </div>

function validateForm() {
         var x = document.getElementById("txtEmail").value;
         var atpos = x.indexOf("@");
         var dotpos = x.lastIndexOf(".");
         if (atpos < 1 || dotpos < atpos + 2 || dotpos + 2 >= x.length) {


             document.getElementById("lblError").innerHTML = "Enter valid email Address";
         }
         else {
             document.getElementById("lblError").innerHTML = "";
         }
     }