Pseudo-Random UUID Generation with mask support


There are a lot of cases where we may want to generate a pseudo-random universally unique identifier (UUID), sometimes called GUID.
I previously wrote an article on creating Pseudo Random numbers in JavaScript, which generates a uuid of length X where x is a numeric value supplied.

http://pragmatic-coding.blogspot.com/2012/01/javascript-pseudo-random-id-generator.html

The problem with the above generator is that is does not allow developers the flexibility of specifying the format of the uuid as shown below:

'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxx0'

'xxxx-xxxx-xxxx-4xxx-yxxx-xxxxxxxxxxx'

'xxxxxxxx-xxxx-xxxx-yxxx-xxxxx-xxxxxx'

Above I’ve shown you 3 different uuid formats that 3 different developers wanted, so an algorithm had to be devised that allow developers the flexibility of changing the data formats.

One other thing to note about the above is the x values, which represents the values you want to be randomly generated. All other values, such as the numeric 4 or 0 are constant values that will be included in all GUID generation.


    /*
     * Returns a random string used for state
     */
    var uuid = function() {
        return genUuid('xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxx0');
    }
   
    /*
     * Returns a random string in the format of a mask
     */
    var genUuid = function(mask) {
        return mask.replace(/[xy]/g, function(c) {
                var r = Math.random()*16|0, v = c == 'x' ? r : (r&0x3|0x8);
                return v.toString(16);
            });    
    }

 NB: Adding fixed values reduces the uniqueness of the generation and hence weakens the effectiveness of the algorithm. 

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