murmurhash2.js

function doHash(str, seed) {
  var m = 0x5bd1e995;
  var r = 24;
  var h = seed ^ str.length;
  var length = str.length;
  var currentIndex = 0;
  
  while (length >= 4) {
    var k = UInt32(str, currentIndex);
    
    k = Umul32(k, m);
    k ^= k >>> r;
    k = Umul32(k, m);

    h = Umul32(h, m);
    h ^= k;

    currentIndex += 4;
    length -= 4;
  }
  
  switch (length) {
  case 3:
    h ^= UInt16(str, currentIndex);
    h ^= str.charCodeAt(currentIndex + 2) << 16;
    h = Umul32(h, m);
    break;
    
  case 2:
    h ^= UInt16(str, currentIndex);
    h = Umul32(h, m);
    break;
    
  case 1:
    h ^= str.charCodeAt(currentIndex);
    h = Umul32(h, m);
    break;
  }

  h ^= h >>> 13;
  h = Umul32(h, m);
  h ^= h >>> 15;

  return h >>> 0;
}

function UInt32(str, pos) {
  return (str.charCodeAt(pos++)) +
         (str.charCodeAt(pos++) << 8) +
         (str.charCodeAt(pos++) << 16) +
         (str.charCodeAt(pos) << 24);
}

function UInt16(str, pos) {
  return (str.charCodeAt(pos++)) +
         (str.charCodeAt(pos++) << 8);
}

function Umul32(n, m) {
  n = n | 0;
  m = m | 0;
  var nlo = n & 0xffff;
  var nhi = n >>> 16;
  var res = ((nlo * m) + (((nhi * m) & 0xffff) << 16)) | 0;
  return res;
}

function getBucket(str, buckets) {
  var hash = doHash(str, str.length);
  var bucket = hash % buckets;
  return bucket;
}

Here is an MIT-licensed Javascript implementation of MurmurHash 2 and 3: https://github.com/garycourt/murmurhash-js

See also the Wikipedia page on MurmurHash, which currently links to these two implementations.