A single regular expression replace should do it:
var stringWithSmallIntegers = "4° 7' 34"W, 168° 1' 23"N";
var paddedString = stringWithSmallIntegers.replace(
/\d+/g,
function pad(digits) {
return digits.length === 1 ? '0' + digits : digits;
});
alert(paddedString);
shows the expected output.