uuid v4 regex

uuidv4test.js

import { v4 as uuid } from 'uuid';

export function generateId() {
  return uuid();
}

const v4 = new RegExp(/^[0-9A-F]{8}-[0-9A-F]{4}-4[0-9A-F]{3}-[89AB][0-9A-F]{3}-[0-9A-F]{12}$/i);

console.log(generateId().match(v4));
//console.log(generateId().length)
//console.log('new way')
//console.log(generateId().length)
//console.log('new way, chopped')
//console.log(generateId().split('-')[0])
//console.log('old way')
//const generateNumber = () => Math.ceil(Math.random() * 100)
//console.log(`${generateNumber()}${generateNumber()}${generateNumber()}${generateNumber()}`)
// run with $ node_modules/.bin/babel-node testuuid.js

The trailing /i means a case insensitive search. RE the last two comments.

@juanmartinez-viamericas A capture group (the parentheses) is not allowed in a range (the brackets), so your regex allows to put parentheses and pipres in uuids. And your "insensitive regex without flag" doesn't allow this range [89ab] in uppercase.

/^[0-9(a-f|A-F)]{8}-[0-9(a-f|A-F)]{4}-4[0-9(a-f|A-F)]{3}-[89ab][0-9(a-f|A-F)]{3}-[0-9(a-f|A-F)]{12}$/
  .test('376)5f8c-e686-4b(9-a85b-7e31|8f4062c') // returns true
//          ^            ^           ^
/^[0-9(a-f|A-F)]{8}-[0-9(a-f|A-F)]{4}-4[0-9(a-f|A-F)]{3}-[89ab][0-9(a-f|A-F)]{3}-[0-9(a-f|A-F)]{12}$/
  .test('376a5f8c-e686-4b79-A85b-7e31e8f4062c') // returns false
//                          ^

Using regex to support upper/lowercase is totally bonkers. If you expect it to be uppercase / not, assert that the string is uppercase / not . If you don't know, just normalize your data first. Pointed out by @Mars073 the lower/upper regex also adds unnecessarily complexity that can break things