Implementing an IsNumeric Function

Javascript does not have a built-in isNumeric function.  Instead a function must be implemented. In this article we shall illustrate one method where we check the characters in the passed string against a pre-defined list.

Two methods are used within the function charAt and indexOf. 

The charAt method is used to find out which character is in a designated position within the string. The indexOf method is then used to search theValidChars list of valid characters. If the character doesn't exist in the list, if ValidChars.indexOf(Char) == -1, then an invalid character is in the supplied string, sText, and the function is aborted, returning false.

function IsNumeric(sText) {
   var ValidChars = "0123456789.";
   var Char;
   for (i = 0; i < sText.length; i++) {
       Char = sText.charAt(i);
       if (ValidChars.indexOf(Char) == -1) {
          return= false;
       }
    }
   return IsNumber;
}

The above function may also be used to check for a valid set of characters, simply by changing the content of the string ValidChars. The following function will also work, although perhaps a little less obviously.

function isNumeric(sText) {
return !/\D/sText
}

This version of the function uses regular expresssions, it test to see whether the string sText contains any non-numeric characters.