js: alpha numeric string pattern test

strnumstrnum.js

// recursive function to test if string follows a pattern
// of repeating single alpha > numeric or numeric > alpha characters

function strnum(s) {
	function iter(t, i) {
		if(i > s.length - 1) return true;
		else {
			if(t === 1) {
				if(!isNaN(s[i])) return false;
				else return iter(2, i += 1);
			}
			else if(t === 2) {
				if(isNaN(parseInt(s[i], 10))) return false;
				else return iter(1, i += 1);
			}
			else return false;
		}
	}
	if(!isNaN(s[0])) {
		return iter(2, 0);
	} else {
		return iter(1, 0);
	}
}