CODEWITHSUNDEEP
javascriptguid
springathing
springathing

Reputation: 475

Javascript GUID (Global Unique Identifier) Generator Explanation

I'm trying to write a JavaScript GUID generator for 8 characters including lowercase / uppercase letters, numbers and symbols. I found these solutions but need an explanation on what is happening in each. Originally I thought I'd need a string holding all the letters/numbers/symbols that I would index into with random number function to build a new GUID, but these solutions seem to create numbers/letters/symbols out of thin air.

In solution 1, what is the purpose of "1+" and "0x10000"? What is the purpose of ".toString(16)" and ".substring(1)" and how is it generating numbers/symbols/AND letters with just that little bit of code?

Solution 1:

function guid() {
  function s4() {
    return Math.floor((1 + Math.random()) * 0x10000)
      .toString(16)
      .substring(1);
  }
  return s4() + s4() + '-' + s4() + '-' + s4() + '-' +
    s4() + '-' + s4() + s4() + s4();
}

In solution 2, I see how the GUID is 32 characters long but don't understand why Math.Random is being multiplied by specifically "16", with a toString(16) attached but no ".substring(x)" this time?

Solution 2:

function generateGuid() {
  var result, i, j;
  result = '';
  for(j=0; j<32; j++) {
    if( j == 8 || j == 12|| j == 16|| j == 20) 
      result = result + '-';
    i = Math.floor(Math.random()*16).toString(16).toUpperCase();
    result = result + i;
  }
  return result;
}

No need to explain the structure of a GUID nor what is a hyphen is XD

Any and all detailed explanations are appreciated!

Upvotes: 1

Views: 14427

Answers (1)

marvel308
marvel308

Reputation: 10458

In the 2nd case Math.random() would generate a number which lies between 0(inclusive) to 1(exclusive).
Now if I want a number which should be < 16, multiplying 16 with a value in [0, 1) should do the job for me, toString(16) converts it into a digit of base 16. We add 32 such digits overall

The 1st example generates a number between (1.0, 2.0] and multiplies it with (10^4) to the base 16. Now we have a number in the range (10000, 20000] base 16.

taking the last 4 digits should suffice for us so we take the relevant substring out of it.
That being the case I think 

Math.floor((Math.random()) * 0x10000)
  .toString(16)

would also suffice for that solution, since we need a 4 digit hexa number

Upvotes: 5

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