Save any form to autofill for development, supports dynamic content with {{ Math.random() }} syntax

bookmarklet.js

http://kolodny.github.io/bookmarklet.html

document.body.addEventListener('click', go);
alert('click on a form element to get a bookmarklet of the saved form');

function go(event) {
  var form = event.target;
  while (form && form.tagName !== 'FORM') {
    form = form.parentNode;
  }
  if (!form) {return;}
  event.preventDefault();
  document.body.removeEventListener('click', go);

  var formSelector;
  if (form.id) {
    formSelector = '#' + form.id;
  } else if (form.name) {
    formSelector = 'form[name="' + form.name + '"]';
  } else {
    formSelector = 'form:nth-child(' + (Array.prototype.indexOf.call(document.forms, form) + 1) + ')'
  }
  var bookMarkletCode = "var form = document.querySelector('" + formSelector + "');\nvar inputIndex = -1;\nvar input;\n\n";
  Array.prototype.forEach.call(form, function(elem, i) {
    var code;
    switch (elem.type) {
      case 'reset':
      case 'button':
      case 'reset':
        code = '';
        break;
      case 'select-multiple':
        var selectedArray = Array.prototype.map.call(elem.options, function(option, i) {
          return option.selected ? 1 : 0;
        });
        code = JSON.stringify(selectedArray) + '.forEach(function(selected, optionIndex) {\n\tinput.options[optionIndex].selected = !!selected\n})';
        break;
      case 'select-one':
        code = 'input.selectedIndex = ' + elem.selectedIndex + ';';
        break;
      case 'radio':
      case 'checkbox':
        code = 'input.checked = ' + (elem.checked ? 'true' : 'false') + ';';
        break;
      default:
        code = 'input.value = ' + JSON.stringify(elem.value).replace(/\{\{(.*?)\}\}/g, '" + $1 + "') + ';';
    }
    
    bookMarkletCode += 'input = form[++inputIndex]; /* input[' + i + '] */\n' + code + '\n\n';
  });
  var a = document.createElement('a');
  a.href = 'javascript:(function(){\n' + escape(bookMarkletCode) + '\n})();'
  a.innerText = 'Form Filler';
  a.style.position = 'fixed';
  a.style.top = 0;
  a.style.left = 0;
  a.style.zIndex = 99999;
  a.style.background = 'green';
  a.style.color = 'white'
  a.style.padding = '10px';
  a.onclick = function() {
    document.body.removeChild(a);  
  };
  document.body.insertBefore(a, document.body.firstChild);
  alert('the bookmarklet is available at the top left of the page, drag to bookmarks bar to add, click to remove from DOM');
}