resize_jenkins_editor.js

// ==UserScript==
// @name         Resizeable Jenkins Script Editor
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Display pipeline options in wide screen, make script editor resizeable.
// @author       Andrew Allen (credit to Victor Toulouse for previous version)
// @match        http://jenkins-ci.org
// @grant        none
// ==/UserScript==

/**
 * Wait for the script editor to appear.
 */
function check(changes, observer) {
  var ace_editors = document.querySelectorAll('.ace_editor');
  ace_editors.forEach(function(editor) {
    if(!editor.made_wide) {
      var container = editor.closest('tr.dropdownList-container');
      if(container) {
        container.querySelector(':scope > td:nth-child(1)').style.display = 'none';
        container.querySelector(':scope > td:nth-child(2)').colSpan = '3';
        editor.made_wide = true;
      }
    }

    if(!editor.made_resizeable) {
      var jquery_ui = editor.closest('.jquery-ui-1');
      if(jquery_ui) {
        jquery_ui.style.resize = 'both';
        jquery_ui.style.overflow = 'scroll';
        jquery_ui.style.height='750px';
        editor.style.height='100%';
        const resizeObserver = new ResizeObserver(entries => {
          for (let entry of entries) {
            if(entry.target.aceEditor) entry.target.aceEditor.resize();
          }
        });
        resizeObserver.observe(editor);
        editor.made_resizeable = true;
      }
    }
  });
}

(function() {
  'use strict';

  document.querySelector('.container').style.width = '100%';
  document.querySelector('.container').style.padding = '0';
  document.querySelector('.col-md-offset-2').style.width = '100%';
  document.querySelector('.col-md-offset-2').style.margin = '0';

  (new MutationObserver(check)).observe(document, {childList: true, subtree: true});

})();

@a2int, thanks for the help. Using Jenkins 2.176.1 unfortunately does not works.