hashmap
a javascript hashmap implementation that handles key collisions
Disclaimer
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...
Install
npm install --save hashmap-js
Description
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.
Usage
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.
API
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
testing
to run the test you'll need to install the development dependencies:
npm install
then to run the tests:
npm test