A JavaScript function for validating whether a given string of characters represents a number of the given base (binary or decimal).

binOrDecCheck.js

/*********************************************************
 * Checks whether a given string represents a number of
 * the given base. For example, 1101 is base 2. 
 * @param {String} digitString 
 * @param {String} base 
 * @return {Boolean} true if digitString matches base
 ********************************************************/
 function validateInput( digitString, base ) {
  
   // Determine the cardinality of the digitSet.
   var digitSet = [];
   if ( base == "2" ) 
     digitSet = ['0', '1'];
   else 
     digitSet = ['0','1','2','3','4','5','6','7','8','9'];
     
   /**
    * For each character in digitString,
    * check whether the character is a member 
    * of the digitSet for the given base.
    * Return false if not.
    */
   for ( var i in digitString ) {
     var charMatch = false;
    	for (var k in digitSet ) {
    	  if ( digitString[i] == digitSet[k] ) 
    			  charMatch = true;
    	}
    	if (!charMatch) 
    	  return false;
  	}

   /**
    * If all the characters in digitString are
    * members of digitSet, then return true.
    */
   return true;
 }