How to grab values from a multiple select dropdown menu and send them along with POST?

When you submit a form, it passes an array to the next page, specified in the form's action attribute. If one isn't set, it will submit to the current URL.

By default, forms will submit using GET unless set the method attribute to post.

So, change your <form> tag to the following:

<form method="post" action="test.php">

And give your select a name, like name="test_select".

And then your test.php can look like this:

<?php
  print_r($_POST);

(no need for a ?> closing tag)

This will print the $_POST array and you'll see how multiple selects work.

You made a few mistakes in your HTML: This is the corrected version:

<form action="test2.php" method="post">
    <select name="example2[]" id="example2" multiple="multiple" >
        <div id="otherChoices" name="hello">
            <optgroup label="Academic" class="blah">
                <option value="Engineering" class="blah">Engineering</option>
                <option value="Humanities">Humanities</option>
                <option value="Life_Sciences">Life Sciences</option>
                <option value="Social Sciences_Sciences">Social Sciences</option>
            </optgroup>
            <optgroup label="Clubs">
                <option value="Event">Event </option>
                <option value="Meeting">Meeting</option>
                <option value="Performance">Performance</option>
            </optgroup>
            <optgroup label="Personal">
                <option value="Discussion">Discussion</option>
                <option value="Event">Event</option>
                <option value="Food">Food</option>
                <option value="Hangout">Hangout</option>
                <option value="Trip">Trip</option>
            </optgroup>
        </div>
    </select>
    <button type="submit">Submit</button>
</form>

EDIT: This is what I corrected:

1. I added a name value to the select with square brackets to show its an array
2. I added a method type to the form: method="post"
3. Submit button

You can then access the individual items like this:

echo $_POST["example2"][0];

EDIT: Sorry I realised this is Node.js That one was for PHP. See this link for how to get post variable in node js:

How do you extract POST data in node.js?