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Transit is a data format and a set of libraries for conveying values between applications written in different languages. This library provides support for marshalling Transit data to/from ClojureScript. Unlike the Java and Clojure implementations it relies on the non-streaming JSON parsing mechanism of the host JavaScript environment.

This implementation's major.minor version number corresponds to the version of the Transit specification it supports.

NOTE: Transit is intended primarily as a wire protocol for transferring data between applications. If storing Transit data durably, readers and writers are expected to use the same version of Transit and you are responsible for migrating/transforming/re-storing that data when and if the transit format changes.

Releases and Dependency Information


Add the following to your project.clj :dependencies:

[com.cognitect/transit-cljs "0.8.280"]


Maven dependency information:



(ns example
  (:require [cognitect.transit :as t]))

(defn roundtrip [x]
  (let [w (t/writer :json)
        r (t/reader :json)]
    (t/read r (t/write w x))))

(defn test-roundtrip []
  (let [list1 [:red :green :blue]
        list2 [:apple :pear :grape]
        data  {(t/integer 1) list1
               (t/integer 2) list2}
        data' (roundtrip data)]
    (assert (= data data'))))

Default Type Mapping


  • cc = cljs.core
  • gm = goog.math
  • cct = com.cognitect.transit
Transit type Write accepts Read returns
null null null
string String String
boolean Boolean Boolean
integer Number, gm.Long Number, gm.Long
decimal Number Number
keyword cc.Keyword cc.Keyword
symbol cc.Symbol cc.Symbol
big integer cct.TaggedValue cct.TaggedValue
big decimal cct.TaggedValue cct.TaggedValue
time Date Date
uri cct.URI cct.URI
uuid cct.UUID cct.UUID
char String String
array cc.IVector cc.IVector
list cc.IList cc.IList
set cc.ISet cc.ISet
map cc.IMap cc.IMap
link cct.Link cct.Link
cmap cct.IMap cct.IMap


This library is open source, developed internally by Cognitect. We welcome discussions of potential problems and enhancement suggestions on the transit-format mailing list. Issues can be filed using GitHub issues for this project. Because transit is incorporated into products and client projects, we prefer to do development internally and are not accepting pull requests or patches.



Install dependencies with

lein deps

Running the tests & benchmarks

Running the tests:

lein cljsbuild once test

In order to run the transit-format bin/verify you must first clone transit-format into the same parent directory as your transit-cljs checkout and build the roundtrip file:

lein cljsbuild once roundtrip

To run the benchmarks you must first clone transit-format into the same parent directory as your transit-cljs checkout.

Running the benchmarks:

lein cljsbuild once bench
node target/transit.bench.js


Build JAR for ClojureScript

Assuming you have a JDK and Maven installed, the following will install a JAR suitable for use from ClojureScript into your local Maven repository.


Copyright and License

Copyright © 2014-2022 Cognitect

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.