Get the return value of a HTML Form Post method

Question

You need to make an AJAX request. Although not strictly necessary, I would suggest you to use jQuery, it will make things a lot easier. Please also have a look at this question: jQuery AJAX submit form

Here's a little example in Mason, it's very simplified of course, you should add some error checking and some escaping also, but I think it could be a good start. Your A.mc component could look like this:

<html>
<head>
  <title>This is A</title>
  <script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
  <script>
  $(document).ready(function() {

    $("#myform").submit(function() { // intercepts the submit event
      $.ajax({ // make an AJAX request
        type: "POST",
        url: "B", // it's the URL of your component B
        data: $("#myform").serialize(), // serializes the form's elements
        success: function(data)
        {
          // show the data you got from B in result div
          $("#result").html(data);
        }
      });
      e.preventDefault(); // avoid to execute the actual submit of the form
    });

  });
  </script>
</head>
<body>
  <form id="myform">
  <input type="text" name="mytext" />
  <input type="submit" />
  </form>

  <div id="result"></div>
</body>
</html>

it's just an HTML page that loads jQuery library and that contains your form, and that contains some code to instruct the form to make an AJAX request to B component when the user clicks the Submit button and then to show the contents returned by B component in your result div.

And this could be your B.mc component:

<%class>
  has 'mytext';
</%class>
I got this text <strong><% $.mytext %></strong> from your form,
and its length is <strong><% length($.mytext) %></strong>.

Result will be like this:

enter image description here