Version 2 API only.

`addListener`

Method Signature	void ultraCart.addListener(String event, function);
Description	Registers a function as a listener to an ultraCart event
Parameter	String event - the name of the event. Events are listed and discussed in the init() method documentation.
Parameter	function - a javascript function. The function will not be passed any parameters.
Result	no return value

see removeListener and fire

function doSomethingWhenShippingChanges(){
    alert('shipping choice changed!');
}

ultraCart.addListener(ultraCart.events.EVENT_SHIPPING_CHANGE, doSomethingWhenShippingChanges);

addListener (JS API v2)

addListener

`addListener`