Compare two strings accounting for multi-digit numbers

strnatcasecmp.js

/**
 * Compare two strings accounting for multi-digit numbers
 * @param {(string|number)} a First string to compare
 * @param {(string|number)} b Second string to compare
 * @return {number} 0 if they match, -1 if a comes before b, +1 if b comes before a
 */
function strnatcasecmp(a, b) {
	a = ("" + a).toLowerCase();
	b = ("" + b).toLowerCase();

	var a_char, a_index = 0, a_num, a_len, a_length = a.length,
			b_char, b_index = 0, b_num, b_len, b_length = b.length,
			isDigit = function(c) {
				var charCode = c.charCodeAt(0);
				return (charCode >= 48 && charCode <= 57); // 0-9
			};

	while (a_index < a_length && b_index < b_length) {
		a_char = a.charAt(a_index++);
		b_char = b.charAt(b_index++);

		if (isDigit(a_char) && isDigit(b_char)) {
			a_num = a_len = b_num = b_len = 0;
			do {
				a_len++;
				a_num = a_num * 10 + parseInt(a_char, 10);
				a_char = a.charAt(a_index++);
			} while (isDigit(a_char));
			a_index--; // Last character isn't eaten
			do {
				b_len++;
				b_num = b_num * 10 + parseInt(b_char, 10);
				b_char = b.charAt(b_index++);
			} while (isDigit(b_char));
			b_index--; // Last character isn't eaten
			if (a_num === b_num) {
				a_char = a_len;
				b_char = b_len;
			} else {
				a_char = a_num;
				b_char = b_num;
			}
		}
		if (a_char < b_char) {
			return -1;
		} else if (a_char > b_char) {
			return 1;
		}
	}
	return a_length === b_length ? 0 : a_length < b_length ? -1 : 1;
}