javascript isNaN() function not working? -


i have function test if prompt input number, so:

function myfunction()  {     var person = prompt("please enter name", "");      if (person != null)      {         if(isnan(person))         {             document.write("hello " + person + "<br><br>");         }         else             document.write("you gave me number");      }     else     {         document.write("you didn't answer.<br><br>");     } }

but every time enter number keeps outputting hello + number. i've been googling function quite time , doesn't make sense me, seems should work. why person returning true?

nan special value in javascript. isnan check see if value passed equal* special value. if want check if is, say, not stream of numbers, can use regular expression:

if (!/^\d+(\.\d+)?/.exec(person)) {

or parse value number , see if converts same string:

var n = parsefloat(person); if (n.tostring() !== person) {

*there's reason don't use === it's outside scope of answer.


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