Simple and easy to understand bloom filter in javascript for the browser. Uses BigInts and crypto.subtle.digest in 29 lines

bloomFilterBigint.js

/**
Simple and fast bloom filter (about 40 lines of actual code)
Uses build-in hash and BigInts to do work. Hash requires async/await
Meant for use in browser code not node

used like this:

// add to bloom
const bloomFilter = new BloomFilter();
bloomFilter.loadSaved();  // optional loading from localstorage
await bloomFilter.add("test1");
await bloomFilter.add("test2");
...
// check for values later
const found = await.bloomFilter.contains("test1"); // MAY be in bloom
const notFound = await.bloomFilter.contains("test3"); // Definitely NOT in bloom
...
bloomFilter.save(); // optional save

**/
class BloomFilter {
  // may use 'SHA-256' for better distribution
  constructor(shaStr='SHA-1') {
    this.bloomBigInt = BigInt(0);
    this.encoder = new TextEncoder(); // performance
    this.shaStr = shaStr;
  }

  async hash(item) {
    // hash into buffer
    const hashBuffer = await crypto.subtle.digest(this.shaStr, // e.g.'SHA-1'
      this.encoder.encode(item));
    // hash buffer to bigint passes through hex string. must be a better way?
    const hashArray = Array.from(new Uint8Array(hashBuffer));
    const hashHex = hashArray
     .map((b) => b.toString(16).padStart(2, "0"))
     .join("");
    return BigInt(`0x${hashHex}`);
  }

  async add(item) {
    const bn = await this.hash(item);
    this.bloomBigInt = bn | this.bloomBigInt;
  }

  async contains(item) {
    const bn = await this.hash(item);
    return (bn & this.bloomBigInt) === bn;
  }

  // the save/restore could use some work
  save() {
    localStorage.setItem(`bloomSha1`, this.bloomBigInt.toString());
  }

  loadSaved() {
    const loadedBitsStr = localStorage.getItem(`bloomSha1`) || '';
    if (loadedBitsStr?.length) {
      this.bloomBigInt = BigInt(loadedBitsStr);
    }
  }
}