Some version parsing, generating, and comparison functions

gistfile1.js

// If a string begins with 'v' and ends with a dotted sequence of numbers,
// return an array of those numbers. Otherwise, return null.
// Examples:
// 'v1'     -> [ 1 ]
// 'v1.2'   -> [ 1, 2 ]
// 'v1.2.3' -> [ 1, 2, 3 ]
// '1.2.3'  -> null
function parseVersion (v) {
	function parseDecInt (a) {
		return parseInt(a, 10);
	}

	var result = /^v(\d+(?:\.\d+)*)$/.exec(v);
	return result
		   ? result[1].split('.').map(parseDecInt)
		   : null;
}

// The inverse operation of parseVersion: given an array of numbers, return a
// string beginning with 'v' and ending with the sequence of numbers in dotted
// format.
function generateVersion (v) {
	return 'v' + v.reduce(function (p, v) {
		// Force numbers to be integers with |0 so we don't end up with floating
		// points in the version string. Perhaps paranoid?
		return (p|0).toString() + '.' + (v|0);
	});
}

// Compare two arrays of numbers lexicographically. Return less than zero if a
// is ordered before b, greater than zero if b is ordered before a, and zero if
// the two arguments compare equal. If one array is a prefix of the other, the
// shorter of the two arrays is ordered before the longer. Suitable for use
// with Array.sort().
function lexicographicCompare (a, b) {
    for (var i = 0; i < Math.max(a.length, b.length); ++i) {
        if (a[i] != b[i]) {
            return undefined === a[i] || a[i] < b[i]
                   ? -1 : 1;
        }
    }
    return 0;
}

// Choose the maximum version among an array of version arrays and return it.
function maxVersion (versions) {
	function chooseGreaterVersion (p, v) {
		return lexicographicCompare(p, v) > 0 ? p : v;
	}

	var versionArrays = versions.map(parseVersion).filter(Boolean);
	return versionArrays.length
		   ? generateVersion(versionArrays.reduce(chooseGreaterVersion))
		   : null;
}

// Split a filename into its stem and extension, if present. The extension's
// dot is retained to distinguish no extension from an empty extension.
// Examples:
// 'a.b.c' -> { stem: 'a.b', extension: '.c' }
// 'a.'    -> { stem: 'a',   extension: '.' }
// 'a'     -> { stem: 'a',   extension: null }
function splitFilename (a) {
	var i = a.lastIndexOf('.');
	return i > 0
		   ? { stem: a.slice(0, i), extension: a.slice(i) }
		   : { stem: a.slice(0),    extension: null };
}