Playing around creating combinations from number based on dic

test.js

const exec = require('child_process').exec;

var letters = " abcdefghijklmnopqrstuvxz".split("");
var args = process.argv.slice(2);

function number_to_word(number) {
  let result = "";
  while (number > 0 ) {
    let pos = number % letters.length;
    let char = letters[ pos ];
    number -= pos;
    number /= letters.length;
    result = char + result;
  }
  return result.trim();
}

function test_word_thread(current_word,thread=0,call_next=false){
  const word = current_word + thread;
  const password = number_to_word(word);
  if ( password.indexOf(" ") > -1 ) {
    if( call_next ) {
      test_word(word,thread);
    }
    return;
  }
  const child = exec(`qpdf --decrypt --password=${password} doc.pdf decrypted-filename.pdf`,
      (error, stdout, stderr) => {
          if (error == null ) {
              console.log(`password: ${password}`);
              process.exit();
          } else {
             if( word % 1000 == 0 ) {
               console.log(`current_word = ${word} `,password)
             }
             if( call_next ) {
               test_word(word,thread);
             }
          }
  });

}

function test_word(current_word,total_threads=8) {
  for(current_thread = 1; current_thread <= total_threads; current_thread++ ) {
    test_word_thread(current_word,current_thread,total_threads==current_thread);
  }
}
test_word(1 * args[0]);