How to Create GUID / UUID in JavaScript?

A Globally Unique Identifier (GUID) or Universally Unique Identifier (UUID) is a 128-bit value used as a unique identifier in software development. It's typically represented as a 32-character hexadecimal string with hyphens, like: de305d84-75c4-431d-acc2-eb6b0e5f6014. Here are several JavaScript methods to generate GUIDs/UUIDs.

Using Random Number Generation

The most common approach uses Math.random() to generate a UUID v4 format:

function generate_uuidv4() {
   return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g,
   function(c) {
      var uuid = Math.random() * 16 | 0, v = c == 'x' ? uuid : (uuid & 0x3 | 0x8);
      return v.toString(16);
   });
}

for(var i = 0; i < 5; i++) {
   console.log("A sample GUID / UUID:", generate_uuidv4());
}

A sample GUID / UUID: 3b869420-6618-43dd-a351-6373ed8ffb48
A sample GUID / UUID: 5d3459b9-d5f1-49ca-a356-d315b314b7eb
A sample GUID / UUID: 19d3ea72-24c7-46e8-177c-a052eb9bc677
A sample GUID / UUID: e3f70fb6-951a-4ee1-b3a2-3173bf7e3a91
A sample GUID / UUID: eac986d7-2d1d-40a4-29eb-92eb131bd0cc

Enhanced Method with Timestamp

To reduce collision probability, we can incorporate the current timestamp:

function generate_uuidv4() {
   var dt = new Date().getTime();
   return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g,
   function(c) {
      var rnd = Math.random() * 16; // random number in range 0 to 16
      rnd = (dt + rnd) % 16 | 0;
      dt = Math.floor(dt / 16);
      return (c === 'x' ? rnd : (rnd & 0x3 | 0x8)).toString(16);
   });
}

for(var i = 0; i < 5; i++) {
   console.log("A sample GUID / UUID:", generate_uuidv4());
}

A sample GUID / UUID: 7a83193c-9624-48e2-a223-e910878c89c5
A sample GUID / UUID: c8e49a59-16a4-4d22-97fc-cdafffba2707
A sample GUID / UUID: 7feea4a6-59d5-4f0e-b7b7-b5cd2069fa0f
A sample GUID / UUID: f244e83c-5af5-483b-8fdd-39d56c6b16ee
A sample GUID / UUID: bc2e2167-91d5-4f53-afc3-af9efdc14e56

Using Pseudo-Random Character Generation

This method manually constructs a UUID by generating random hexadecimal characters and placing them in the correct positions:

function generate_uuidv4() {
   var id_str = [];
   var hxDigits = "0123456789abcdef";
   
   for (var i = 0; i < 36; i++) {
      id_str[i] = hxDigits.substr(Math.floor(Math.random() * 0x10), 1);
   }
   
   id_str[14] = "4"; // version field
   id_str[19] = hxDigits.substr((id_str[19] & 0x3) | 0x8, 1); // variant field
   id_str[8] = id_str[13] = id_str[18] = id_str[23] = "-"; // hyphens
  
   return id_str.join("");
}

for(var i = 0; i < 5; i++) {
   console.log("A sample GUID / UUID:", generate_uuidv4());
}

A sample GUID / UUID: b5106962-5bc5-46dc-b74e-7a3fd0584fc0
A sample GUID / UUID: 5fdfa0e1-4251-4ae6-bafc-b162e032ab48
A sample GUID / UUID: de644da7-2dc4-499f-82fa-618f5b6f133e
A sample GUID / UUID: cc5ce77f-18dd-46ba-8762-1cc7cf9c7a7f
A sample GUID / UUID: 1708db50-0d8d-4fcc-8e7e-5cfc23387c6f

Simple Random String Method

A faster but less standard-compliant approach generates random alphanumeric strings:

function generate_simple_uuid() {
   return Math.random().toString(36).substring(2, 15) +
          Math.random().toString(36).substring(2, 15);
}

for(var i = 0; i < 5; i++) {
   console.log("A sample GUID / UUID:", generate_simple_uuid());
}

A sample GUID / UUID: 8kyxdvlm8by3licwpf081c
A sample GUID / UUID: coemu70fbbw9e8gsvvw8aq
A sample GUID / UUID: 41kamutwz52izjiw1h769
A sample GUID / UUID: r3e4app5nfsphj3wa7sa8
A sample GUID / UUID: 463olfnw767sr9hy0hlcn

Comparison of Methods

Conclusion

For most applications, the random number generation method with timestamp enhancement provides the best balance of standard compliance and collision resistance. Use the simple string method only when performance is critical and uniqueness requirements are less strict.