Can not check blank selection field while submitting form using PHP and Javascript -

i have 1 issue while submitting form can not check blank selection field.i explaining code below.

addcomplain.php:

    <form name="billdata" id="billdata"  enctype="multipart/form-data" method="post" onsubmit="javascript:return checkform();">        <div class="input-group bmargindiv1 col-md-12">         <span class="input-group-addon ndrftextwidth text-right" style="width:180px"> name :</span>          <input type="text" name="u_name" id="name" class="form-control" placeholder="add name" onkeypress="clearfield('name');">         </div>          <div class="input-group bmargindiv1 col-md-12">         <span class="input-group-addon ndrftextwidth text-right" style="width:180px">email :</span>         <input type="email" name="u_email" id="emailid" class="form-control" placeholder="add email id" onkeypress="clearfield('emailid');">          </div>         <div class="input-group bmargindiv1 col-md-12">          <span class="input-group-addon ndrftextwidth text-right" style="width:180px">type of complaint      :</span>         <select class="form-control"  id="compleant" name="complaintype" onchange="javascript:checkcomfield();">          <option value="">select types of complaint</option>          <option value="card">card related</option>          <option value="claim">claim related</option>          <option value="product">product related</option>          <option value="premimum">premimum related</option>         </select>         </div> <input type="submit" class="btn btn-success" name="complainsubmit"  id="addprofiledata" value="add"/>     </form> <script>     function checkform(){         var s=document.billdata;         console.log('compalin',s.complaintype.value=='');         if(s.u_name.value==''){             alert('please enter name');             s.u_name.focus();             s.u_name.style.bordercolor = "red";             return false;         }else if(s.u_email.value==''){             alert('please enter email');             s.u_email.focus();             s.u_email.style.bordercolor = "red";             return false;         }else if(! validateemail(s.u_email.value)){             alert('please enter valid email');             s.u_email.focus();             s.u_email.style.bordercolor = "red";             return false;         }else if(s.complaintype.value==''){             alert('please select type of complain');             s.complaintype.focus();             s.complaintype.style.bordercolor = "red";             return false;         }else{         }     } </script> 

here problem when have value in name , email field , no value select selection field, clicking on add button form submitting blank selection field can not check.here need check blank field before submit.please me.

i checked code. throwing errors in console. functions clearfield , validateemail not defined. commented out these functions , working fine.

here demo same.

you can add functions clearfield , validateemail , check afterwards code working or not.

in demo have added these functions , working fine.