$ npm install semver

semver.valid('1.2.3') // '1.2.3'
semver.valid('a.b.c') // null
semver.clean('  =v1.2.3   ') // '1.2.3'
semver.satisfies('1.2.3', '1.x || >=2.5.0 || 5.0.0 - 7.2.3') // true
semver.gt('1.2.3', '9.8.7') // false
semver.lt('1.2.3', '9.8.7') // true

As a command-line utility:

$ semver -h

Usage: semver -v <version> [-r <range>]
Test if version(s) satisfy the supplied range(s),
and sort them.

Multiple versions or ranges may be supplied.

Program exits successfully if any valid version satisfies
all supplied ranges, and prints all satisfying versions.

If no versions are valid, or ranges are not satisfied,
then exits failure.

Versions are printed in ascending order, so supplying
multiple versions to the utility will just sort them.

A version is the following things, in this order:

• a number (Major)
• a period
• a number (minor)
• a period
• a number (patch)
• OPTIONAL: a hyphen, followed by a number (build)
• OPTIONAL: a collection of pretty much any non-whitespace characters (tag)

A leading "=" or "v" character is stripped off and ignored.

The ordering of versions is done using the following algorithm, given two versions and asked to find the greater of the two:

• If the majors are numerically different, then take the one with a bigger major number. 2.3.4 > 1.3.4
• If the minors are numerically different, then take the one with the bigger minor number. 2.3.4 > 2.2.4
• If the patches are numerically different, then take the one with the bigger patch number. 2.3.4 > 2.3.3
• If only one of them has a build number, then take the one with the build number. 2.3.4-0 > 2.3.4
• If they both have build numbers, and the build numbers are numerically different, then take the one with the bigger build number. 2.3.4-10 > 2.3.4-9
• If only one of them has a tag, then take the one without the tag. 2.3.4 > 2.3.4-beta
• If they both have tags, then take the one with the lexicographically larger tag. 2.3.4-beta > 2.3.4-alpha
• At this point, they're equal.

The following range styles are supported:

• >1.2.3 Greater than a specific version.
• <1.2.3 Less than
• 1.2.3 - 2.3.4 := >=1.2.3 <=2.3.4
• ~1.2.3 := >=1.2.3 <1.3.0
• ~1.2 := >=1.2.0 <1.3.0
• ~1 := >=1.0.0 <2.0.0
• 1.2.x := >=1.2.0 <1.3.0
• 1.x := >=1.0.0 <2.0.0

Ranges can be joined with either a space (which implies "and") or a || (which implies "or").

• valid(v): Return the parsed version, or null if it's not valid.
• inc(v, release): Return the version incremented by the release type (major, minor, patch, or build), or null if it's not valid.

• gt(v1, v2): v1 > v2
• gte(v1, v2): v1 >= v2
• lt(v1, v2): v1 < v2
• lte(v1, v2): v1 <= v2
• eq(v1, v2): v1 == v2 This is true if they're logically equivalent, even if they're not the exact same string. You already know how to compare strings.
• neq(v1, v2): v1 != v2 The opposite of eq.
• cmp(v1, comparator, v2): Pass in a comparison string, and it'll call the corresponding function above. "===" and "!==" do simple string comparison, but are included for completeness. Throws if an invalid comparison string is provided.
• compare(v1, v2): Return 0 if v1 == v2, or 1 if v1 is greater, or -1 if v2 is greater. Sorts in ascending order if passed to Array.sort().
• rcompare(v1, v2): The reverse of compare. Sorts an array of versions in descending order when passed to Array.sort().

• validRange(range): Return the valid range or null if it's not valid
• satisfies(version, range): Return true if the version satisfies the range.
• maxSatisfying(versions, range): Return the highest version in the list that satisfies the range, or null if none of them do.