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This project is part of the @thi.ng/umbrella monorepo.


Vector clock functions for synchronizing distributed states & processes.

Vector clock algorithm:

  • Initially all clocks are zero.
  • Each time a process experiences an internal event, it increments its own logical clock in the vector by one (inc()).
  • Each time a process sends a message, it increments its own logical clock in the vector by one and then sends a copy of its own vector.
  • Each time a process receives a message, it increments its own logical clock in the vector by one and updates each element in its vector by taking the maximum of the value in its own vector clock and the value in the vector in the received message (merge()).

The package provides the following immutable vector clock operations, where vector clocks are plain JS objects:

  • inc(clock, id) - increment (or create) clock component
  • remove(clock, id) - remove clock component
  • merge(a, b) - merge two vector clocks
  • signedSkew(a, b) - max signed difference between vector clocks
  • absSkew(a, b) - max unsigned difference between vector clocks
  • compare(a, b) - comparator for logically ordering vector clocks
  • isBefore(a, b) - true if a < b
  • isAfter(a, b) - true if a > b
  • isConcurrent(a, b) - if both clocks represent concurrent updates
  • equiv(a, b) - equality predicate
  • orderAsc(a, b) - alias for compare()
  • orderDesc(a, b) - reverse order to orderAsc()



BETA - possibly breaking changes forthcoming

Search or submit any issues for this package


yarn add @thi.ng/vclock
// ES module
<script type="module" src="https://unpkg.com/@thi.ng/vclock?module" crossorigin></script>

// UMD
<script src="https://unpkg.com/@thi.ng/vclock/lib/index.umd.js" crossorigin></script>

Package sizes (gzipped, pre-treeshake): ESM: 478 bytes / CJS: 558 bytes / UMD: 614 bytes



Generated API docs



Karsten Schmidt

If this project contributes to an academic publication, please cite it as:

  title = "@thi.ng/vclock",
  author = "Karsten Schmidt",
  note = "https://thi.ng/vclock",
  year = 2018


© 2018 - 2021 Karsten Schmidt // Apache Software License 2.0

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