How can I get form data with JavaScript/jQuery?

Question

Is there a simple, one-line way to get the data of a form as it would be if it was to be submitted in the classic HTML-only way?

For example, in:

<form>
 <input type="radio" name="foo" value="1" checked="checked" />
 <input type="radio" name="foo" value="0" />
 <input name="bar" value="xxx" />
 <select name="this">
  <option value="hi" selected="selected">Hi</option>
  <option value="ho">Ho</option>
</form>

Out:

{
 "foo": "1",
 "bar": "xxx",
 "this": "hi"
}

Something like this is too simple, since it does not (correctly) include textareas, selects, radio buttons and checkboxes:

$("#form input").each(function() {
 data[theFieldName] = theFieldValue;
});

Answer 1

Here is a working JavaScript only implementation which correctly handles checkboxes, radio buttons, and sliders (probably other input types as well, but I've only tested these).

function setOrPush(target, val) {
    var result = val;
    if (target) {
        result = [target];
        result.push(val);
    }
    return result;
}

function getFormResults(formElement) {
    var formElements = formElement.elements;
    var formParams = {};
    var i = 0;
    var elem = null;
    for (i = 0; i < formElements.length; i += 1) {
        elem = formElements[i];
        switch (elem.type) {
            case 'submit':
                break;
            case 'radio':
                if (elem.checked) {
                    formParams[elem.name] = elem.value;
                }
                break;
            case 'checkbox':
                if (elem.checked) {
                    formParams[elem.name] = setOrPush(formParams[elem.name], elem.value);
                }
                break;
            default:
                formParams[elem.name] = setOrPush(formParams[elem.name], elem.value);
        }
    }
    return formParams;
}

Working example:

    function setOrPush(target, val) {
      var result = val;
      if (target) {
        result = [target];
        result.push(val);
      }
      return result;
    }

    function getFormResults(formElement) {
      var formElements = formElement.elements;
      var formParams = {};
      var i = 0;
      var elem = null;
      for (i = 0; i < formElements.length; i += 1) {
        elem = formElements[i];
        switch (elem.type) {
          case 'submit':
            break;
          case 'radio':
            if (elem.checked) {
              formParams[elem.name] = elem.value;
            }
            break;
          case 'checkbox':
            if (elem.checked) {
              formParams[elem.name] = setOrPush(formParams[elem.name], elem.value);
            }
            break;
          default:
            formParams[elem.name] = setOrPush(formParams[elem.name], elem.value);
        }
      }
      return formParams;
    }

    //
    // Boilerplate for running the snippet/form
    //

    function ok() {
      var params = getFormResults(document.getElementById('main_form'));
      document.getElementById('results_wrapper').innerHTML = JSON.stringify(params, null, ' ');
    }

    (function() {
      var main_form = document.getElementById('main_form');
      main_form.addEventListener('submit', function(event) {
        event.preventDefault();
        ok();
      }, false);
    })();

<form id="main_form">
  <div id="questions_wrapper">
    <p>what is a?</p>
    <div>
      <input type="radio" required="" name="q_0" value="a" id="a_0">
      <label for="a_0">a</label>
      <input type="radio" required="" name="q_0" value="b" id="a_1">
      <label for="a_1">b</label>
      <input type="radio" required="" name="q_0" value="c" id="a_2">
      <label for="a_2">c</label>
      <input type="radio" required="" name="q_0" value="d" id="a_3">
      <label for="a_3">d</label>
    </div>
    <div class="question range">
      <label for="a_13">A?</label>
      <input type="range" required="" name="q_3" id="a_13" min="0" max="10" step="1" list="q_3_dl">
      <datalist id="q_3_dl">
        <option value="0"></option>
        <option value="1"></option>
        <option value="2"></option>
        <option value="3"></option>
        <option value="4"></option>
        <option value="5"></option>
        <option value="6"></option>
        <option value="7"></option>
        <option value="8"></option>
        <option value="9"></option>
        <option value="10"></option>
      </datalist>
    </div>
    <p>A and/or B?</p>
    <div>
      <input type="checkbox" name="q_4" value="A" id="a_14">
      <label for="a_14">A</label>
      <input type="checkbox" name="q_4" value="B" id="a_15">
      <label for="a_15">B</label>
    </div>
  </div>
  <button id="btn" type="submit">OK</button>
</form>
<div id="results_wrapper"></div>

edit:

If you're looking for a more complete implementation, then take a look at this section of the project I made this for. I'll update this question eventually with the complete solution I came up with, but maybe this will be helpful to someone.