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A simple bridge to ClojureScript's persistent data structures and supporting APIs for vanilla JavaScript. Pull requests welcome.

Breaking changes in 0.3.0

This release includes several breaking changes:

  • More idiomatic JavaScript API naming scheme
  • No EDN reader
  • No zippers
  • No data diffing

These missing options will likely find their way back into Mori when Mori builds can leverage Google Closure Modules.

Getting it

You can install the latest release via npm:

npm install mori

The installed package contains a single optimized JavaScript file mori.js.

Load mori in your Node.js programs as you would any other module:

var mori = require("mori");

In a browser, you can load mori with a script tag, as you would any other JavaScript library:

<script src="mori.js" type="text/javascript"></script>

You can also load it as an AMD module, e.g. with RequireJS.



You will first need to install the Java SDK, if it's not already installed on your system.

On Windows, you will need to manually install Leiningen. On UNIX-like systems, Leiningen will be installed within the project automatically if the lein executable is not found on your path or if your lein version predates 2.0.0.

Clone the repo

git clone
cd mori

On a UNIX-like system build with


Alternatively using npm

npm run-script build

On Windows


The build process will generate an optimized JavaScript file mori.js, which is suitable for use with Node.js, or in a Web browser or other JavaScript environments. You can also load it as an AMD module.


You can use it from your projects like so:

var inc = function(n) {
  return n+1;
mori.intoArray(, mori.vector(1,2,3,4,5)));
// => [2,3,4,5,6] 

Efficient non-destructive updates!

var v1 = mori.vector(1,2,3);
var v2 = mori.conj(v1, 4);
v1.toString(); // => '[1 2 3]' 
v2.toString(); // => '[1 2 3 4]' 
var sum = function(a, b) {
  return a + b;
mori.reduce(sum, mori.vector(1, 2, 3, 4)); // => 10 

Lazy sequences!

var _ = mori;
_.intoArray(_.interpose("foo", _.vector(1, 2, 3, 4)));
// => [1, "foo", 2, "foo", 3, "foo", 4] 

Or if it's more your speed, use it from CoffeeScript!

inc = (x) -> x+1  
= incmori.vector(1,2,3,4,5)
mori.intoArray r


You can find extensive documentation and examples here.

More Examples

Efficient Freeze/Thaw

For vectors and maps we provide an efficient thaw and freeze operations:

var m = mori;
// ~220ms with V8 version 3.29.80 MBP 2.26ghz 
for(var j = 0; j < 10; j++) {
  var s = new Date();
  var arr = [];
  for(var i = 0; i < 10000000; i++) {
  print("Array push " + arr.length + " items " + ((new Date())-s));
// ~70ms 
for(var j = 0; j < 10; j++) {
  s = new Date();
  var mv = m.mutable.thaw(m.vector());
  for(var i = 0; i < 10000000; i++) {
    mv = m.mutable.conj.f2(mv, i);
  var v = m.mutable.freeze(mv);
  print("Mutable vector conj " + m.count(v) + " items " + ((new Date())-s));

ES6 Map/Set inspired interfaces

All Mori maps and sets support all the non-mutating methods of the proposed ES6 Map and Set interfaces. The main difference with the spec is that key lookup is based on value not reference. keys, values, and entries methods return the proposed mutable iterators:

var m = mori;
var h = m.hashMap("foo", 1, "bar", 2);
h.has("foo"); // => true 
h.get("foo"); // => 1 
var iter = h.keys();; // => {done: false, value: "foo"} 

This feature is subject to changes in the ES6 proposal.


Mori includes Transducers. Zero allocation collection operations FTW:

var m = mori;
var a = [];
for(var i = 0; i < 1000000; i++) {
// make it immutable 
var v = m.into(m.vector(), a);
function time(f) {
  var s = new Date();
  console.log(((new Date())-s)+"ms");
// ~190ms V8 version 3.29.80 MBP 2.26ghz 
time(function() {
  var xf = m.comp(,,;
  return m.transduce(xf, m.completing(m.sum), 0, v);
}, 10);
// ~440ms 
time(function() {
  return,b){return a+b;}, 0);
}, 10);

Copyright (C) 2012-2015 David Nolen and contributors

Distributed under the Eclipse Public License, the same as Clojure.