# JavaScript generation algorithm for GUID

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A globally unique identifier (GUID, Globally Unique Identifier) is also called UUID(Universally Unique IDentifier) .

GUID is a digital identifier generated by the algorithm of binary length of 128 bits. GUID format for “ xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx”, where x is 0-9 or A-F within the scope of a 32 bit hexadecimal number sixteen. In the ideal case, any computer and computer cluster will not generate the same two GUID.

The total number of GUID reached 2^128 (3.4× 10^38), so the possibility of a randomly generated two of the same GUID is very small, but not 0. GUID a word sometimes refers specifically to the Microsoft on the UUID standard.

Algorithm 1

```function uuid() {
var s = [];
var hexDigits = "0123456789abcdef";
for (var i = 0; i <36; i++) {
s[i] = hexDigits.substr(Math.floor(Math.random() * 0x10), 1);
}
s[14] = "4";  // bits 12-15 of the time_hi_and_version field to 0010
s[19] = hexDigits.substr((s[19] & 0x3) | 0x8, 1);  // bits 6-7 of the clock_seq_hi_and_reserved to 01
s[8] = s[13] = s[18] = s[23] = "-";

var uuid = s.join("");
return uuid;
}
```

Algorithm 2

```function guid() {
return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
var r = Math.random()*16|0, v = c == 'x' ? r : (r&0x3|0x8);
return v.toString(16);
});
}
```

Algorithm 3

```function guid() {
function S4() {
return (((1+Math.random())*0x10000)|0).toString(16).substring(1);
}
return (S4()+S4()+"-"+S4()+"-"+S4()+"-"+S4()+"-"+S4()+S4()+S4());
}
```

Algorithm 4

```function uuid(len, radix) {
var chars = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'.split('');
var uuid = [], i;

if (len) {
// Compact form
for (i = 0; i <len; i++) uuid[i] = chars[0 | Math.random()*radix];
} else {
// rfc4122, version 4 form
var r;

// rfc4122 requires these characters
uuid[8] = uuid[13] = uuid[18] = uuid[23] = '-';
uuid[14] = '4';

// Fill in random data.  At i==19 set the high bits of clock sequence as
// per rfc4122, sec. 4.1.5
for (i = 0; i <36; i++) {
if (!uuid[i]) {
r = 0 | Math.random()*16;
uuid[i] = chars[(i == 19) ? (r & 0x3) | 0x8 : r];
}
}
}

return uuid.join('');
}
```

This can specify the length and base. For example

```// 8 character ID (base=2)
uuid(8, 2)  //  "01001010"
// 8 character ID (base=10)
uuid(8, 10) // "47473046"
// 8 character ID (base=16)
uuid(8, 16) // "098F4D35"
```

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Posted by Joanna at November 14, 2013 - 6:53 PM