Export Special:EditWatchlist’s state before submitting the page

exportWatchlist.js

( function() {
  let list = '';
  for ( let checkbox of document.querySelectorAll( 'input[type=checkbox]' ) ) {
    let checked = checkbox.checked,
        title = checkbox.value,
        labelElement = checkbox.nextElementSibling.querySelector( 'a' ),
        text;
    if ( !labelElement ) {
      labelElement = checkbox.nextElementSibling;
    }
    text = labelElement.textContent;
    list += checked + '\t' + title + '\t' + text + '\n';
  }
  let output = document.createElement( 'pre' );
  output.textContent = list;
  document.body.appendChild( output );
  console.log( 'done' );
} )();