js-exercises/ejer12/12.js

function main() {
  var palabra = document.getElementById('numeroDeLetras').value;

  for (let a = 0; a < palabra.length; a++) {

    for (let i = 0; i <= a; i++) {
      document.writeln(`${palabra[i]}`);
    }
    document.writeln(`<br>`)

  }
}