问否则永远不会执行

EN

function FillInfo()
{
         /* proměnné */
         var jmeno = document.forms ["SignUpForm"] ["jmeno"].value;
         var prijmeni = document.forms ["SignUpForm"] ["prijmeni"].value;
         var rok = document.forms ["SignUpForm"] ["mesto"].value;
         /*Kontrola zdali input políčka jsou prázdná či pokud bylo zadáno číslo */
         if(jmeno=="" || jmeno!=NaN || prijmeni=="" ||  prijmeni!= NaN || mesto=="" || mesto!=NaN){  

            document.getElementById("info").innerHTML = "Please fill out all of available boxes and make sure there are no numbers";    
      }
         else{     

            document.getElementById("info").innerHTML =  "Thank you" + " " + jmeno + " " + prijmeni + " from" + " " + mesto + "." + " " + "You are now being considered as our next adventurer. Good luck!";
    }
 }

<div class="heading2">
        <div class="container2">
            <p>Do you want to travel troughout space? Then fill out our form!</p><br>
            <form name="SignUpForm">
                <input type="text" name="jmeno" placeholder="First name" required><br>
                <input type="text" name="prijmeni" placeholder="Last name" required><br>
                <input type="text" name="mesto" placeholder="City" required><br><br>
                <div id="info" class="well"></div>
                <input type="button" class="otherpage" onclick="FillInfo();" value="Submit" /><br><br>
                <a href="Mainpage.html" class="BeginLink">Return</a>
            </form>  
       </div>      
    </div>