"dropdown-button" with variations

As long as you can add the following to the form that you are creating you should be fine:

onchange="ReadForm (this.form, false);"

It is basically calling a JavaScript function named “ReadForm”

Thankyou, I was hoping it would be that easy!

Out of curiousity:
Do I need to make my edits in the plugin-file or is this something I can put in my functions-file, for future updates I mean?

*starstruck*

Still cant get it to work and I think it is partly because this new dropdown button needs to also be the submit-button?

Also I get this error in the console:
TypeError: ‘undefined’ is not an object (evaluating ‘obj1.length’)

This is the output of my button:

<div class="wp_cart_button_wrapper btn">
	<form method="post" class="wp-cart-button-form" action="" style="display:inline" onsubmit="return ReadForm(this, true);">
		<div class="btn-group">
			<a name="variation1" onchange="ReadForm(this.form, false);" class="btn dropdown-toggle" data-toggle="dropdown" >Add to cart <span class="caret"></span></a>
			<ul class="dropdown-menu">
				<li><a value="S ">S </a></li>
				<li><a value=" M "> M </a></li>
				<li><a value=" L"> L</a></li>
				</ul>
				</div>
				<br />

				<input class="btn" type="submit" value="Add to Cart" />
				<input type="hidden" name="product" value="En helt ny" />
				<input type="hidden" name="price" value="14" />
				<input type="hidden" name="product_tmp" value="En helt ny" />
				<input type="hidden" name="shipping" value="10" />
				<input type="hidden" name="cartLink" value="https://localhost/wordpress/shop-merchandise/" />
				<input type="hidden" name="addcart" value="1" />
		</form>
</div>

If I add a normal button below to submit it sends without the variation..