On submission function is not being called in custom module
Could you try like this:

function my_form($form, &amp;$form_state) {
  $pl_name=array();
  $pl_name=getplaylist_to_edit(arg(1));

  $form['text'] = array(
    '#type' =&gt; 'textfield',
    '#id'=&gt;'edit-playlist-name',
    '#value' =&gt; $pl_name[1],
  );

  $form['submit'] = array(
    '#type' =&gt; 'submit',
    '#value' =&gt; 'Update',
  );

  return $node;
}

function my_form_submit($form, &amp;$form_state){
  echo '&lt;script&gt;alert("You have submitted the form.");&lt;/script&gt;';
}