html - uncaught reference error Function not defined Javascript -

simple program calculate periodic interest rate, function defined , called in button still error uncaught reference still shows. appreciated

function calculatepayment(){         var loanamount = document.getelementbyid("txtloanamount").value;         var interestrate = document.getelementbyid("txtinterestrate").value;         var amortiperiod = document.getelementbyid("txtyearlyperiod").value;         var totalpayment;         var numofmonths;          //convert strings text box integers         loanamount = parseint(loanamount);         interestrate = parseint(interestrate);         amortiperiod = parseint(amortiperiod);         //validate input boxes ensure values added , follow application rules         if (loanamount == null || loanamount == ""){             //alert("you must enter loan amount");             message = "you must enter loan amount";             document.getelementbyid("errormessage").innerhtml = message;         }else if (interestrate == null || interestrate == ""){             //alert("you must enter interest rate");             message = "you must enter interest rate";             document.getelementbyid("errormessage").innerhtml = message;         }else if (amortiperid == null || amortiperiod == ""){             //alert("you must enter interest rate");             message = "you must enter interest rate";             document.getelementbyid("errormessage").innerhtml = message;          }else if isnan(loanamount || interestrate || amortiperiod){             message = "the values enter must numeric";             document.getelementbyid("errormessage").innerhtml = message;          }else{             numofmonths = amortiperiod * 12;             paymentrate = loanamount * interestrate / 100;             totalpayment = paymentrate * numofmonths;             message = totalpayment;             document.getelementbyid("errormessage").innerhtml = message;          }      } 

here html:

<tr>                 <td><input type="button" onclick="calculatepayment()" name="btncalculate" value="calculate payment"/></td><td><input type="button" name="btnclear" value="clear"/></td>             </tr> 

unexpected identifier:

  } else if isnan(loanamount || interestrate || amortiperiod) { 

with markup (since provide less needed)

<input id="calcme" type="button" name="btncalculate" value="calculate payment" /> <input type="button" name="btnclear" value="clear" /> <input type="text" id="txtinterestrate" value="10">int <input type="text" id="txtloanamount" value="1200">amt <input type="text" id="txtyearlyperiod" value="1"> years per <div id="errormessage">   errors </div> 

you need revise partially working code solve real problems here:

function showerror(message) {   document.getelementbyid("errormessage").innerhtml = message; }  function showloanamount(amount) {   document.getelementbyid("txtloanamount").value = amount; }  function showinterestrate(rate) {   document.getelementbyid("txtinterestrate").value = rate; }  function showyearlyperiod(period) {   document.getelementbyid("txtloanamount").value = period; }  function getloanamount() {   return parseint(document.getelementbyid("txtloanamount").value); }  function getinterestrate() {   return parseint(document.getelementbyid("txtinterestrate").value); }  function getyearlyperiod() {   return parseint(document.getelementbyid("txtloanamount").value); }  function calculatepayment() {   // values   var loanamount = getloanamount();   var interestrate = getinterestrate();   var amortiperiod = getyearlyperiod();   var totalpayment;   var numofmonths;   var message = "";    //set values   showloanamount(loanamount);   showinterestrate(interestrate);   showyearlyperiod(amortiperiod);   //validate input boxes ensure values added , follow application rules   if (!loanamount) {     message = "you must enter loan amount";     showerror(message);   }   if (!interestrate) {     message = "you must enter interest rate";     showerror(message);   }   if (!amortiperiod) {     message = "you must enter interest rate";     showerror(message);   }   if (isnan(loanamount) || isnan(interestrate) || isnan(amortiperiod)) {     message = "the values enter must numeric";     showerror(message);   }   // crappy math here   numofmonths = amortiperiod * 12;   paymentrate = loanamount * interestrate / 100;   totalpayment = paymentrate * numofmonths;   message = totalpayment;   showerror(message);  } var el = document.getelementbyid("calcme"); el.addeventlistener("click", calculatepayment, false);