Check and Validate(inline validation) input field when onblur and onfocus.

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 = "";
          }
      }

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