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A JavaScript implementation of Hash data structure. As far as this module is concerned, a Hash is a key-value pair list of items of the same type. It supports all primitive JavaScript types and arbitrary Objects.

Use node-hash when you have a list of items of the same type stored by key, and you don't want to check types in you application code. You need to provide your own comparator function and node-hash will throw when it fails. Generic comparator function for all JavaScript primitive types are exported as object on Hash.comparator.

This implementation doesn't try to substitute the ES6 map implementation, it just represents a lightweight alternative implementation.

Current Version: 1.1.0
Build Status: Build Status
Node Support: 0.8, 0.10, 0.11


npm install node-hash


The keys cannot be defined dynamically, but must be defined at construct time, since the library uses Object.defineProperty to define getters and setters correctly. The constructor also takes a comparator function used to check the value inserted into the Hash. You might also set an initial value to all keys, passing the third parameter.

Hash of Date

var assert = require('assert');
var Hash = require('node-hash');
var times = new Hash(
  ['created_at', 'last_seen', 'last_modified', 'future_action_at'],
  new Date()
// uses a predefined setter which will use the `comparator` function to check the value type
times.created_at = new Date();
times.last_seen = new Date();
times.last_modified = new Date();
// these will all throw
assert.throws( function() { times.last_seen = 'yesterday' } );
assert.throws( function() { times.last_seen = 100 } );
assert.throws( function() { times.last_seen = [] } );
// uses a predefined getter
console.log( times.created_at );
// Fri Aug 08 2014 11:31:04 GMT+0100 (BST)
// returns the internal key-value store
console.log( times.getData() );
  created_at: Fri Aug 08 2014 11:31:04 GMT+0100 (BST),
  last_seen: Fri Aug 08 2014 11:31:04 GMT+0100 (BST),
  last_modified: Fri Aug 08 2014 11:31:04 GMT+0100 (BST),
  future_action_at: Fri Aug 08 2014 11:31:04 GMT+0100 (BST)
// returns all the keys passed to the contructor
assert( times.keys(), ['created_at', 'last_seen', 'last_modified', 'future_action_at'] );
// returns the value of the removed key, or false if the key is not used
times.remove( 'last_modified' );
// returns the number of keys
assert( times.length, 4 );
// resets the hash

Hash of number

var Hash = require( 'node-hash' );
var dailyStats = new Hash(
  ['min', 'max', 'avg', 'samples'],
dailyStats.min = 0;
dailyStats.min = 10;
dailyStats.samples = 1000;
dailyStats.avg = 4.3445345;


A member function that converts a node-hash into a plain Javascript object ready to be serialized. A custom marhall function can be passed as argument.

var hash = new Hash(
  ['key1', 'key2', 'key3'],
hash.key1 = new Date();
// {key1: new Date()}
// {key1: timestamp}
hash.marshall( function (date) {
  return date.getTime();


A static non-member function that converts a plain Javascript object into a node-hash using Hash.unmarshall. A custom unmarshall function can be passed as argument.

// data is a node-hash
var data = Hash.unmarshall(
  { key1: new Date(2013, 0, 1) },
// data is a node-hash
var data = Hash.unmarshall(
  { key1: (new Date(2013, 0, 1)).getTime() },
  function (time) {
    return new Date(time);


npm test


The dev dependencies are coffee-script, mocha and should. The coffeescript is compiled down to javascript automatically before publishing using the 'prepublish' script in 'package.json'. coffeescript files and test files are deliberately left out of the package via '.npmignore' because no one likes needlessly big modules.

Contributions are welcome!