32 bit FNV-1a hash

/**
 * Calculate a 32 bit FNV-1a hash
 *
 * @param {string} str the input value
 * @param {boolean} [asString=false] optionally set to true to return the hash value as 
 *     8-digit hex string instead of an integer
 * @param {integer} [seed=0x811c9dc5] optionally pass the hash of the previous chunk
 * @returns {integer | string}
 */
function hashFnv32a(str, asString = false, seed = 0x811c9dc5) {
  let hval = seed
  for (let i = 0; i < str.length; i++) {
    hval ^= str.charCodeAt(i)
    hval += (hval << 1) + (hval << 4) + (hval << 7) + (hval << 8) + (hval << 24)
  }
  if (asString) {
    // Convert to 8 digit hex string
    return ('0000000' + (hval >>> 0).toString(16)).substr(-8)
  }

  return hval >>> 0
}

In an answer to this question Which hashing algorithm is best for uniqueness and speed?, Ian Boyd posted a good in depth analysis. In short (as I interpret it), he comes to the conclusion that MurmurHash is best, followed by FNV-1a.
Java’s String.hashCode() algorithm that esmiralha proposed seems to be a variant of DJB2.

• FNV-1a has a a better distribution than DJB2, but is slower
• DJB2 is faster than FNV-1a, but tends to yield more collisions
• MurmurHash3 is better and faster than DJB2 and FNV-1a (but the optimized implementation requires more lines of code than FNV and DJB2)

Some benchmarks with large input strings here: http://jsperf.com/32-bit-hash
When short input strings are hashed, murmur's performance drops, relative to DJ2B and FNV-1a: http://jsperf.com/32-bit-hash/3

So in general I would recommend murmur3.
See here for a JavaScript implementation: https://github.com/garycourt/murmurhash-js

If input strings are short and performance is more important than distribution quality, use DJB2 (as proposed by the accepted answer by esmiralha).

If quality and small code size are more important than speed, I use this implementation of FNV-1a (based on this code).

Source: https://stackoverflow.com/questions/7616461/generate-a-hash-from-string-in-javascript-jquery

• hash
• javascript