JavaScript : isNumberic

method 1 :
isNaN()
return false : "-0.5",-100
return true : "string"

method 2 :
check positive Numberic
var ValidChars = "0123456789.-";
reference from http://www.codetoad.com/javascript/isnumeric.asp

The simplest way to check whether the details entered in a text field are numeric is to to loop through the string and compare each character to a pre-defined list of acceptable characters.

In this function, we've allowed decimal points and numbers nought through 9.

We use two methods to help us here : the charAt and indexOf.

Using the charAt method, we can find out which character is filling a designated position within a string. We then use the indexOf method to search our ValidChars list of valid characters. If it doesn't exist, (if ValidChars.indexOf(Char) == -1) this means the user has entered an invalid character. Here's the full function.

function IsNumberic(sText)
{
   var ValidChars = "0123456789.";
   var IsNumber=true;
   var Char;

 
   for (i = 0; i < sText.length && IsNumber == true; i++) 
      { 
      Char = sText.charAt(i); 
      if (ValidChars.indexOf(Char) == -1) 
         {
         IsNumber = false;
         }
      }
   return IsNumber;
   
   }