Stop pretending we can serialize buttons in a form

The library previously serialized all buttons present in a form, saving name and value attributes as key/value pairs. Standard HTML forms do not do this, but save name and value only for the button that was used to submit the form. This change stops serialization for any button data, to avoid the incorrect assumption that the data stem from the submitted button (it doesn't, buttons are serialized sequentially). At some later point, the code might be extended to capture the data for the submitted button, but that would not be an easy change, and popular serialization libraries don't implement this feature for the stated reason.

Author: FelixHenninger

docs/reference/html.rst

@@ -149,6 +149,11 @@ By combining the above code with an :js:class:`html.Form`, it can become part of
 
 The above screen, inserted into an experiment, will display the form, and wait for the user to submit it using the supplied button. When this occurs, the form contents will automatically be transferred into the experiment's data set, and whichever value was entered into the specified field will be saved into the variable ``participant-id``.
 
+.. caution::
+   The :js:class:`html.Form` differs from standard ``HTML`` forms (those that are sent to a server, which responds with a new page) in one important point: It does *not* save information about the ``<button>`` used to submit the ``<form>`` data. This is because the information is not made available within the page itself.
+
+   If you are looking to capture a response to one of several buttons, we recommend using an :js:class:`html.Screen` instead, and defining a distinct :js:attr:`response <options.responses>` for clicks on every button.
+
 .. js:class:: html.Form([options])
 
   An :js:class:`html.Form` accepts the same options and provides the same methods the :js:class:`html.Screen` does, with a few additions:

packages/library/src/html.js

@@ -139,16 +139,6 @@ export class Form extends Screen {
               // no default
             }
             break
-          case 'button':
-            switch (element.type) {
-              case 'button':
-              case 'submit':
-              case 'reset':
-                output[element.name] = element.value
-                break
-              default:
-            }
-            break
           default:
         } // outer switch
       }) // iterate across elements

packages/library/test/html.js

@@ -223,17 +223,6 @@ describe('HTML-based components', () => {
       })
     })
 
-    it('serializes buttons', () => {
-      f.options.el.innerHTML = '' +
-        '<form>' +
-        '  <button name="button" value="value">' +
-        '</form>'
-
-      assert.deepEqual(f.serialize(), {
-        'button': 'value'
-      })
-    })
-
     const exampleForm = '' +
       '<form>' +
       '  <input type="text" name="text_input" value="text_input_contents">' +
@@ -281,7 +270,6 @@ describe('HTML-based components', () => {
       return f.run().then(() => {
         f.submit()
         assert.equal(f.data.text_input, 'text_input_contents')
-        assert.equal(f.data.button, 'value')
       })
     })