Generate randomly in XXXX-0000 format

Question

How to generate a string randomly in the format XXXX-0000 where X can it be a letter or a number? What I have achieved so far is as follows::

var letra = String.fromCharCode(65+Math.floor(Math.random() * 26))
var numero = Math.floor(Math.random() * 9);

Generates a letter, and a random number. However, I do not know how to make a loop of this to stay in the format I want.

Answer 1

You do not need to use repeat structures to generate alphanumeric values. Just use a base in the function toString, for example:

let first = Math.random()       // Gera um valor randômico
                .toString(36)   // Utiliza a Base36
                .substr(-4)     // Captura os 4 últimos números
                .toUpperCase(); // Converte para maiúscula 
                
let last = Math.floor((Math.random() * (9999 - 1000)) + 1000); // Gera um valor entre 999 e 10000

console.log( `${first}-${last}` )

To Base36 is a numerical system consisting of Arabic numerals from 0 to 9 and Latin letters from A to Z, e.g.: 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z (note that letters may be uppercase or lowercase letters).

for (let num = 0; num <= 35; num++) {
  var a = num.toString();   // Decimal
  var b = num.toString(2);  // Binário
  var c = num.toString(8);  // Octal
  var d = num.toString(16); // Hexadecimal
  var e = num.toString(36); // Hexatrigesimal

  var n = a + " | " + b + " | " + c + " | " + d + " | " + e + "<br><br>";

  document.body.innerHTML += n;
}

Answer 2

According to the question, what is desired is that the first 4 characters are alphanumeric and the last 4 numerical only:

          ┌──────┐   ┌──────┐
          │ XXXX │ - │ 0000 │
          └──────┘   └──────┘
              ↑         ↑
     alfanuméricos     numéricos
(números ou letras)

You can use the variable numero to randomly switch the concatenation between letter or number, checking whether numero is par: if it’s par, concatenates a letter; if it is unique, concatenates a number.

Use a bow tie for to generate the 8 characters (4 alphanumerics + 4 numerics):

for(var x=1, alfanum = num = ""; x<5; x++){
   var letra = String.fromCharCode(65+Math.floor(Math.random() * 26));
   var numero = Math.floor(Math.random() * 9);
   var numero2 = Math.floor(Math.random() * 9);
   alfanum += numero%2 == 0 ? letra : numero; // verifico se 'numero' é par para formar a sequência alfanumérica
   num += numero2; // formo a sequência numérica
}
console.log(alfanum+"-"+num);

Answer 3

A functional approach would be like this:

const geraAlpha = () => {
  return String.fromCharCode(65 + Math.floor(Math.random() * 26))
}

const geraNumero = () => {
  return Math.floor(Math.random() * 10)
}

const reduce = Array(4).fill(0).reduce(prev => {
  return {
    alpha: prev.alpha + geraAlpha(), 
    numero: prev.numero+ geraNumero()
  }
}, {alpha: '', numero: ''})

console.log(`${reduce.alpha}-${reduce.numero}`)