function validation()
{
	
	var name = document.getElementById("txtName").value;
    	var emailid = document.getElementById("txtEmail").value;
	var mobile = document.getElementById("txtMobile").value;
	var position = document.getElementById("cmbPosition").value;
		    
   
	if (name == "")
		{
			alert("Please Enter  Name");
			document.getElementById("txtName").focus();
			return false;
		}
	else if(echeck(emailid) == false)
	    {
		  emailid = "";
		  document.getElementById("txtEmail").focus();
		  return false;
		 }
	else if (mobile == "")
		{
			alert("Please Enter Contact Number");
			document.getElementById("txtMobile").focus();
			return false;			
		}
	else if (position == 0)
		{
			alert("Please Select Position");
			document.getElementById("cmbPosition").focus();
			return false;			
		}
	return true;		
}




<!--Mobile validation code -->
function isNumberKey(evt)
      {
	     var charCode = (evt.which) ? evt.which : event.keyCode
         if (charCode > 31 && (charCode < 48 || charCode > 57))
		    {
                alert ("Please Enter Only Numeric Digits For Your Mobile Number!");
				return false;
				}
		 
		  else if(evt.value.length==10)
		     {
			  alert ("Mobile number cannot more than 10 digits");
			  return false;
			  } 
	   return true;
		  
	}	
	
<!--Email validation code -->
 
 function echeck(str) {

		var at="@"
		var dot="."
		var lat=str.indexOf(at)
		var lstr=str.length
		var ldot=str.indexOf(dot)
		if (str.indexOf(at)==-1){
		   alert("Invalid E-mail ID")
		   return false
		}

		if (str.indexOf(at)==-1 || str.indexOf(at)==0 || str.indexOf(at)==lstr){
		   alert("Invalid E-mail ID")
		   return false
		}

		if (str.indexOf(dot)==-1 || str.indexOf(dot)==0 || str.indexOf(dot)==lstr){
		    alert("Invalid E-mail ID")
		    return false
		}

		 if (str.indexOf(at,(lat+1))!=-1){
		    alert("Invalid E-mail ID")
		    return false
		 }

		 if (str.substring(lat-1,lat)==dot || str.substring(lat+1,lat+2)==dot){
		    alert("Invalid E-mail ID")
		    return false
		 }

		 if (str.indexOf(dot,(lat+2))==-1){
		    alert("Invalid E-mail ID")
		    return false
		 }
		
		 if (str.indexOf(" ")!=-1){
		    alert("Invalid E-mail ID")
		    return false
		 }

 		 return true					
	}