Simple string-based one-way hashing algorithm for JavaScript

Question

I've been searching around for a simple-lightweight hashing algorithm for JavaScript. I did find this numerically-based answer on Stack Overflow here.

Unfortunately, I am unable to use this since it's numerically based and I'll need to use this hash as a unique index elsewhere in my code. Often this function returns negative numbers and that would be a big no-no (try 'hello world!'.hashCode() from the snippet linked above to see what I mean).

I've been tempted to use the md5 hashing libraries out there for JS but they're simply to bulky for my purpose and encryption libraries (such as this) are overkill.

It's worth noting that the information within this hash isn't sensitive in anyway and it wouldn't necessarily matter if it was decrypted. The purpose of this function would be to simply generate fixed-length output data that acts as a shortened reference to the original data that I would pass in.

Any help, tips and comments are much appreciated :)

How about Math.abs('hello world!'.hashCode())?

KooiInc
– KooiInc

2013-07-01 09:44:44 +00:00
Commented Jul 1, 2013 at 9:44 — KooiInc
– KooiInc, Commented Jul 1, 2013 at 9:44
@KooiInc Wouldn't that increase collisions two-fold?

zesda
– zesda

2013-07-01 10:46:56 +00:00
Commented Jul 1, 2013 at 10:46 — zesda
– zesda, Commented Jul 1, 2013 at 10:46

user2497624 · Accepted Answer · 2013-07-01 09:55:18Z

0

The solution proposed by Kooilnc, to use the absolute value, should do the tric for you. However, if you want to use a hashing function to generate a reference, i assume that the reference you get should be unique as to match the exact element it was generated from. If this is the case, be aware of collisions. Hashing function can create hashes that are similar even though the original messages are different and we call this a collision. If i remember correctly, SHA-1 is also available for java script and is not all that bulk. Good luck

answered Jul 1, 2013 at 9:55

user2497624

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Comments

tom · Accepted Answer · 2013-07-01 10:13:15Z

0

I am unable to use this since it's numerically based and I'll need to use this hash as a unique index elsewhere in my code.

Hash functions are normally numerically based and are rarely perfect (produce unique keys). I think you need something different:

function GuidGen()
{
    this.items = {};
    this.size = 0;
}

GuidGen.prototype.get = function(str)
{
    if (!(str in this.items))
    {
        this.items[str] = this.size++;
    }
    return this.items[str];
}

// usage:
id = new GuidGen();
id.get("hello world");  // 0
id.get("spam");         // 1
id.get("eggs");         // 2
id.get("hello world");  // 0

answered Jul 1, 2013 at 10:13

tom

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6 Comments

zesda Over a year ago

Sorry, I should have been a bit clearer. Your answer is completely legitimate, but my needs are slightly different. Often there are many string that are similar in my set and these will need distinguishing by adding a timestamp + misc. data. This results in very long strings (often 30 - 40 characters in length). This, unfortunately, is unacceptable, hence my approach to hashing. The hope is that I will be able to have strings produced of a fixed length that would be good enough as unique identifiers.

tom Over a year ago

@zesda Can you elaborate on the usage of these strings? In particular whether or not they are shared across different programs/computers and how long their lifetime is.

zesda Over a year ago

Essentially I have a file uploader written in JS. I'm going to use these strings to reference the files that are uploaded. The issue arises when it comes to referencing these uploaded files on a unique basis. Indexing these file uploads is a messy business because it's an asynchronous process, so I'm using information from the files themselves to generate unique string-based IDs. The information available is type, name, size and last modified dates. But these aren't unique without a timestamp. Hence my ambition to use hashing to reduce string length.

tom Over a year ago

Right. So what's stopping you from using a random number as a 'hash'? You could still get collisions, but that's always going to happen with fixed-length keys (unless you request free IDs from the server).

zesda Over a year ago

Random numbers do not inherit their values from the original data. If I can't replicate the hash elsewhere then how do I reference my file?

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