Generate a Hash from string in Javascript

Question

I need to convert strings to some form of hash. Is this possible in JavaScript?

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

Answer 1

Object.defineProperty(String.prototype, 'hashCode', {
  value: function() {
    var hash = 0, i, chr;
    for (i = 0; i < this.length; i++) {
      chr   = this.charCodeAt(i);
      hash  = ((hash << 5) - hash) + chr;
      hash |= 0; // Convert to 32bit integer
    }
    return hash;
  }
});

Source: http://werxltd.com/wp/2010/05/13/javascript-implementation-of-javas-string-hashcode-method/

Answer 2

I have combined the two solutions (users esmiralha and lordvlad) to get a function that should be faster for browsers that support the js function reduce() and still compatible with old browsers:

String.prototype.hashCode = function() {

    if (Array.prototype.reduce) {
        return this.split("").reduce(function(a,b){a=((a<<5)-a)+b.charCodeAt(0);return a&a},0);   
    } else {

        var hash = 0, i, chr, len;
        if (this.length == 0) return hash;
        for (i = 0, len = this.length; i < len; i++) {
        chr   = this.charCodeAt(i);
        hash  = ((hash << 5) - hash) + chr;
        hash |= 0; // Convert to 32bit integer
        }
        return hash;
    }
};

Example:

my_string = 'xyz';
my_string.hashCode();

Answer 3

This is a refined and better performing variant:

String.prototype.hashCode = function() {
    var hash = 0, i = 0, len = this.length;
    while ( i < len ) {
        hash  = ((hash << 5) - hash + this.charCodeAt(i++)) << 0;
    }
    return hash;
};

This matches Java's implementation of the standard object.hashCode()

Here is also one that returns only positive hashcodes:

String.prototype.hashcode = function() {
    return (this.hashCode() + 2147483647) + 1;
};

And here is a matching one for Java that only returns positive hashcodes:

public static long hashcode(Object obj) {
    return ((long) obj.hashCode()) + Integer.MAX_VALUE + 1l;
}

Enjoy!

Without prototype:

function hashCode(str) {
    var hash = 0, i = 0, len = str.length;
    while ( i < len ) {
        hash  = ((hash << 5) - hash + str.charCodeAt(i++)) << 0;
    }
    return hash;
}

Answer 4

If you want to avoid collisions you may want to use a secure hash like SHA-256. There are several JavaScript SHA-256 implementations.

I wrote tests to compare several hash implementations, see https://github.com/brillout/test-javascript-hash-implementations.

Or go to http://brillout.github.io/test-javascript-hash-implementations/, to run the tests.