SOURCE

   function countNumber(stringtoCount) {
            var numCount  = 0;
            for (var i = 0; i < stringtoCount.length; i++) {
                var char = stringtoCount.charAt(i);
                if (char != " " && !isNaN(char)) {
                    numCount ++;
                }
            }
            return numCount ;
        }
        document.write(countNumber("56ghlkj78"));