1.0.1 • Public • Published


a javascript hashmap implementation that handles key collisions


In my contrived tests, with a fast hash function that produced ~.002% collisions, the HashMap performed ~30% slower than using a plain old object with a toString() function that generated unique strings for each object. So if speed is your aim, this module does not outperform that method, at least not in my testing. Good learning experience for me, probably not that helpful to you...


npm install --save hashmap-js


This module implements a hashmap, which can use objects as keys. You provide the hashing function and a function to determine equality, in the case of collisions.


to initialize, provide your hashing function and equals function:

var HashMap = require( 'hashmap-js' );

var myMap = HashMap( hashFn, equalsFn ),
    value = { test: 'success' };

// add a value
myMap.set( key, value );

// returns value
myMap.get( key );

key can be anything. This module is particularly useful, if you want to use objects as keys and want to handle possible collisions.

hashFn( key )

hashFn is a function that should be able to convert a key to a hash. Traditionally, this would be a number that is calculated by performing some arithmetic on the values of an object that uniquely identify it.

In JavaScript, using a string is reasonable and you could just use a plain old object in this way as long as your toString() function always produced a unique string. The HashMap module is more generic and is most beneficial if you wish to use a more traditional 'hashing' function that returns a number. That being said, Hashmap is perfectly suitable even if you just provide toString() as the hashFn, but again, only provides a benefit if you expect toString() to produce collisions for two non-equivalent objects.

equals( key, otherKey )

this function will be used to compare two keys, in the case that they result in the same value from hashFn.


set( key, value ) - stores the passed value, which will be referenced by the passed key.

get( key ) - returns the value referenced by the passed key, if present

contains( key ) - true if the key is present, otherwise false

remove( key ) - removes the value referenced by the passed key, if present

count() - returns the number of elements in the map

clear() - resets ths map

forEach( onEach ) - iterates over each present value and passes them to the provided callback


to run the test you'll need to install the development dependencies:

npm install

then to run the tests:

npm test

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npm i hashmap-js

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