TOPIC:

<p>My name is 
  <input id="nameField" name="name" type="text" />
  <button id="submitBtn" onclick="submitName()">Submit
  </button>
</p>

for (var i=0; i<x_variables.length; i++) {
  if (x_variables[i].name == 'name') {
    nameVar = i;
    break;
  }
}

function submitName() {
  if ($('#nameField').val() != '') {
    x_variables[nameVar].value = $('#nameField').val();
  }
}

<div id="myForm">
  <p>Name: 
    <input name="name" type="text" />
  </p>
  <p>Email: 
    <input name="email" type="text" />
  </p>
  <p>Course: 
    <input name="course" type="text" />
  </p>
  <button id="submitBtn" onclick="submitForm('myForm')">Submit
  </button>
</div>

function lookupVar(id) {
  for (var i=0; i<x_variables.length; i++) {
    if (x_variables[i].name == id) {
      return i;
      break;
    }
  }
  return null;
}

function submitForm(form) {
  var $inputs = $('#' + form).find('input');
  $inputs.each(function() {
    var id = $(this).attr('name');
    if ($(this).val() != '') {
      	var varIndex = lookupVar(id);
      	if (varIndex != null) {
          x_variables[varIndex].value = $(this).val();
        }
    }
  })
}