Make short hash from long string [duplicate]

Question

I have a very long string and I need a unique ID to cache it. The id doesn't need to be reversed however equal strings need to return the equal id.

For example:

• this-is-a-very-long-string -> SFG2527G
• this-is-something-else -> JSNTFK2783
• this-is-a-very-long-string -> SFG2527G

I don't need to reverse the hash.

What's the best way to achieve this with Javascript?

Answer 1

The shorter the hash, the higher the chances of collision.

However, in the Java world, there is a string hashCode helper that returns a "not so unique" integer out of a string, and it's the smallest way to map a string as ID, but it doesn't guarantee uniqueness and it suffers collisions.

Accordingly, I strongly discourage you to use this in the wild, but for answer sake, here how you can play around with such hash:

function hashCode(s) {
  for (var h = 0, i = 0; i < s.length; h &= h)
    h = 31 * h + s.charCodeAt(i++);
  return h;
}

On the other hand, sha256 is a one way hashing that "doesn't suffer collisions" (it does, but much less than MD5, SHA1, or the hashCode up there), so while the result is a longer unique id, it's kinda granted to always work as expected, and it's explained in MDN.

P.S. NodeJS 15+ has a crypto.webcrypto namespace that is identical to the Web one, so you can use the same code in browsers and server.