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I need to convert strings to some form of hash. In anyway, is this possible in Javascript/jQuery.

I did some Google searches but they all seem to be referring to the # character.

I'm not utilizing a server-side language so I can't do it that way.

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You want to look up something like Javascript md5. – rlemon Sep 30 '11 at 21:55
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3 Answers

up vote 62 down vote accepted 
String.prototype.hashCode = function(){
    var hash = 0, i, char;
    if (this.length == 0) return hash;
    for (i = 0, l = this.length; i < l; i++) {
        char  = this.charCodeAt(i);
        hash  = ((hash<<5)-hash)+char;
        hash |= 0; // Convert to 32bit integer
    }
    return hash;
};

Described here.

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2  
This is the same one used in Java. The hash << 5 - hash is the same as hash * 31 + char but a LOT faster. It's nice because it's so fast, and 31 is a small prime. Win win there. – corsiKa Sep 30 '11 at 21:59
1  
Very lightweight to add on the page too. I like this. Just wondering what resistance to reversing the hashes this has? sequences of numbers for example result in predictable hashes sometimes. – Dan Lehmann Sep 30 '11 at 22:07
5  
I did a few tests on jsperf (jsperf.com/hashing-strings) and the bitwise function is actually more slow than the number based function. – skerit Jun 29 '12 at 21:23
1  
number based is unusable for larger strings. – Peter Aron Zentai Feb 26 at 23:38
1  
@hdgarrood -- Math.pow( 2, 33 ) & <anything> === 0 because the & op does an implicit cast to a 32-bit int and the last 32 bits of that are 0, so the 1 at bit 34 gets thrown away. Anything using the & op will be exactly the same, including & 0xffffffff – cwolves May 31 at 0:19
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up vote 12 down vote

if anyone is interested, here is an improved ( faster ) version, which will fail on older browsers who lack the reduce array function.

hashCode = function(s){
  return s.split("").reduce(function(a,b){a=((a<<5)-a)+b.charCodeAt(0);return a&a},0);              
}
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1  
Much faster. ~ 4 times faster based on my tests. Thanks for the tip. Here's info on browser support for the Array.reduce() method: developer.mozilla.org/en-US/docs/JavaScript/Reference/… – jake May 8 at 2:01
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up vote 0 down vote

I needed a similar function (but different) to generate a unique-ish ID based on the username and current time. So: 

window.newId = ->
  # create a number based on the username
  unless window.userNumber?
  window.userNumber = 0
  for c,i in window.MyNamespace.userName
    char = window.MyNamespace.userName.charCodeAt(i)
    window.MyNamespace.userNumber+=char
  ((window.MyNamespace.userNumber + Math.floor(Math.random() * 1e15) + new Date().getMilliseconds()).toString(36)).toUpperCase()

Produces: 

2DVFXJGEKL
6IZPAKFQFL
ORGOENVMG
... etc
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