Geneate n amount of unique codes containing the characters you specify and write them to a file

generate_codes.js

// Generate X unique codes and write them to a file

// npm install crypto
// node generate_codes.js

var crypto = require('crypto');
var fs = require('fs');

function random (howMany, chars) {
  chars = chars || "ACDEFGHJKMNPQRTWXYZ234679";
  var rnd = crypto.randomBytes(howMany),
      value = new Array(howMany),
      len = chars.length;

  for (var i = 0; i < howMany; i++) {
    value[i] = chars[rnd[i] % len]
  };

  return value.join('');
}

var codefile = fs.openSync('./codes.txt', 'w');

var codes = [];
var code = '';

while(codes.length < 25000) {
  code = random(6);
  if(codes.indexOf(code) < 0) {
    // console.log(code);
    codes.push(code);
    fs.write(codefile, code + '\n');
  } else {
    console.log('dup');
  }
}

fs.closeSync(codefile);