@duckduckgo/jsbloom

#jsbloom


A fast bloom filter implementation in JavaScript using the djb2 and sdbm algorithms.

From _Less Hashing, Same Performance: Building a Better Bloom Filter_ by Adam Kirsch et al, it is possible to build _k_ hash values from only _2_ unique values. Hence, it is sufficient to have two unique hashes generated.

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var filter = new JSBloom(items, false_probability_chance);

filter.addEntry("xyz");

filter.checkEntry("xyz"); // returns true

filter.checkEntry("yz"); // returns false

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Testing is done with mocha and chai

npm install mocha chai
mocha

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items: ceiling of entries to add
false_probability_chance: chance of false positives to occur

JSBloom will automatically generate the needed bit array and amount of hashes needed to meet your requirements.

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addEntry(str): adds str to bloom filter
addEntries(arr): iterates over arr and adds every entry within
checkEntry(str): checks if str in filter, returns false if definitely not, true if maybe
importData(base64, [number_of_hashes]): loads a base 64 LZW compressed Uint8Array
exportData(): returns base 64 encoded Uint8Array LZW as string
exportData(callback): returns the base 64 encoded Uint8Array LZW compressed to provided callback