user script for https://adventofcode.com/ that automatically downloads the input for the day in the format dayDD_input.txt

auto_save_input_to_file.js

Number.prototype.pad = function(size) {
  var s = String(this);
  while (s.length < (size || 2)) {s = "0" + s;}
  return s;
}

if( document.URL.endsWith('/input') )
{
    var url_sans_input = document.URL.slice(0,document.URL.lastIndexOf('/'))
    var day_num = parseInt(url_sans_input.slice(url_sans_input.lastIndexOf('/')+1))

    var bb = new Blob([document.body.innerText], { type: 'text/plain' });
    var a = document.createElement('a');
    a.download = 'day' + day_num.pad(2) + '_input.txt';
    a.href = window.URL.createObjectURL(bb);
    a.click();
}