addRandomCharsBrowser.js

const START_STRING = 'nwlIw6fcI6qf1pmTPuZV1c5SdaIEY2P2Jf9Hf50';
const CHARS_TO_GENERATE = 9;
const CODES_TO_GENERATE = 100;

const POSSIBLE_CHARS = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890';
const TEXTAREA = document.createElement('textarea');
TEXTAREA.cols = 150;
TEXTAREA.rows = 100;
document.body.appendChild(TEXTAREA);

for (let i = 0; i < CODES_TO_GENERATE; i++) {
  let code = START_STRING;
  for (let i = 0; i < CHARS_TO_GENERATE; i++) {
    code += POSSIBLE_CHARS.charAt(Math.floor(Math.random() * POSSIBLE_CHARS.length));
  }
  TEXTAREA.value += (code + '\n');
}