Semver Compare

Semantic versioning gives every release a string like 1.4.2 or 2.0.0-rc.1 together with a precise rule for which release comes first. You are implementing that rule: semverCompare(a, b) parses two version strings and returns -1, 0, or 1 depending on which has the lower precedence. The format is MAJOR.MINOR.PATCH with an optional prerelease tag after a hyphen and optional build metadata after a plus sign. See the Semantic Versioning spec for the full precedence rules.

Signature

semverCompare(a: string, b: string): -1 | 0 | 1
// -1  a has lower precedence than b (a comes first)
//  0  a and b have equal precedence
//  1  a has higher precedence than b

Examples

semverCompare('1.2.3', '1.2.3');         // 0
semverCompare('1.0.10', '1.0.9');        // 1  (10 beats 9 numerically)
semverCompare('1.0.0-alpha', '1.0.0');   // -1 (a prerelease precedes the release)

semverCompare('1.0.0-beta.2', '1.0.0-beta.11');     // -1 (2 is below 11 as numbers)
semverCompare('1.0.0-alpha.1', '1.0.0-alpha.beta');  // -1 (a number ranks below a word)
semverCompare('1.0.0+build.9', '1.0.0');            // 0  (build metadata is ignored)

Notes

• Three numeric fields — compare major, then minor, then patch as numbers, left to right; the first that differs decides the result.
• Prerelease lowers precedence — a version with a prerelease tag comes before the same version without one, so 1.0.0-alpha precedes 1.0.0.
• Identifier rules — split the prerelease on dots and compare left to right: numeric identifiers as numbers, a numeric identifier below a non-numeric one, otherwise by ASCII order; if one tag is a prefix of the other, the tag with more fields wins.
• Build metadata is ignored — everything after the first + has no effect on ordering.
• Well-formed input — you may assume both arguments are valid semver strings; you do not need to reject malformed input.
• Return exactly -1, 0, or 1 — not a raw difference of two numbers.