Generate random N-digit phone number with or without specific prefixes

generate-phone.js

let prefix = ['98', '78', '97', '96', '89', '99', '70', '79', '90', '94', '76', '84', '86', '81'];

function randomInt(a = 0, b = 0) { return (a + window.crypto.getRandomValues(new Uint8Array(1))[0] % Math.abs(b - a)).toString(); }
Uint32Array.prototype.unique = function () { return this.filter((v, i) => ( this.indexOf(v) == i )); }

function numbers(n = 16384, usePrefix, len) {
  let seed = randomInt(0,99999999);
  let numbers = window.crypto.getRandomValues(new Uint32Array(n)).unique();
  numbers.forEach((n) => {
    let pfx = usePrefix ? prefix[n % prefix.length] : '';
    let length = len - pfx.length;
    console.log(pfx + (n*seed).toString().slice(0,length))
  });
  console.log(numbers.length);
}

numbers(150, true, 10);