const chars = 'QWERTYUIOPASDFGHJKLZXCVBNMqwertyuiopasdfghjklzxcvbnm1234567890'.split('');
const codeLength = 7;

const generator = () => {
  const code = [];
  for (let i = 0; i < codeLength; i++) code.push(Math.floor(Math.random() * chars.length));
  return code.join('');
}

const code = generator();
console.log(code);