CAKEPHP Confirming on Submit - forms

Question

I have a submit button in my form like this :
<?php echo $this->Form->end(__('Submit')); ?>
and I want to embed variables that are part of the input form.
For example, I want to embed a variable that is input here $this->Form->input('user_id');.
Does anyone know how to do this? I currently have this onsubmit as part of the options array, but it throws errors when I try to embed variables.
<?php echo $this->Form->create('Shift', array(
'onsubmit' => 'return confirm("Creating shift for '$id' on ");'
)); ?>
Now making an edit to this question. So the Javascript solution worked fine. Issue now is that I want the alert box to display the user's name, which is what is displayed in the dropbox. However, the HTML tags contain the user's ids. Here is the HTML
<div class="input select required">
<label for="my_user_id">User</label>
<select name="data[Shift][user_id]" id="my_user_id" required="required">
<option value="1">john doe</option>
<option value="2">john johnson</option>
Is there a way to access the value between the <option> tags using Javascript?

Answer 1

You need to use double quotes:
<?php
echo $this->Form->create('Shift', array(
'onsubmit' => "return confirm(\"Creating shift for '$id' on \");"
));
?>
Another option is to use $this->Form->postLink() and set $confirmMessage parameter if it is a simple state shift form.

Answer 2

You can use JQuery
echo $this->Form->create('Shift', array('id' => 'myform'));
echo $this->Form->input('user_id', array('id' => 'my_user_id', 'type'=>'text'));
After the form:
<?php echo $this->Html->scriptBlock('
$(document).ready(function() {
$("#myform").submit(function(event) {
alert("Creating shift for " + $("#my_user_id").val());
});
});
');
?>