Magento2 – Trigger Content Update Event in JavaScript

getUrl() function defined in

vendor/magento/module-checkout/view/frontend/web/js/model/resource-url-manager.js

getUrl: function(urls, urlParams) {
            var url;

            if (utils.isEmpty(urls)) {
                return 'Provided service call does not exist.';
            }

            if (!utils.isEmpty(urls['default'])) {
                url = urls['default'];
            } else {
                url = urls[this.getCheckoutMethod()];
            }
            return urlBuilder.createUrl(url, urlParams);
        },

You can use this function just add file path in your define function.

As you pointed out, when you click "Ship here" a HTTP POST request is dispatched to "/V1/carts/mine/estimate-shipping-methods-by-address-id" REST API (from module-quote). If you take a look at module-quote/etc/webapi.xml you will find the url:

<route url="/V1/carts/mine/estimate-shipping-methods-by-address-id" method="POST">
  <service class="Magento\Quote\Api\ShippingMethodManagementInterface" method="estimateByAddressId"/>
  <resources>
    <resource ref="self" />
  </resources>
  <data>
    <parameter name="cartId" force="true">%cart_id%</parameter>
  </data>
</route>

You can notice that under the <route> element there is <service> element with the class="Magento\Quote\Api\GuestShipmentEstimationInterface" and method="estimateByExtendedAddress". Now obviously, the estimateByAddressId method cannot be instantiated from an interface.

Here comes in scene the magento 2 dependency injection. Look at module-quote/etc/di.xml file that maps an interface(Magento\Quote\Api\ShippingMethodManagementInterface) dependency to a preferred implementation class(Magento\Quote\Model\ShippingMethodManagement).

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="Magento\Quote\Api\ShippingMethodManagementInterface" type="Magento\Quote\Model\ShippingMethodManagement" />
    ...................
</config>

This is how estimateByAddressId method is called.

Useful links:

Magento 2 Web APIs:
http://devdocs.magento.com/guides/v2.0/get-started/bk-get-started-api.html
http://devdocs.magento.com/guides/v2.0/extension-dev-guide/service-contracts/service-to-web-service.html

Magento 2 Dependency injection:
http://devdocs.magento.com/guides/v2.0/extension-dev-guide/depend-inj.html
http://magento-quickies.alanstorm.com/post/68129858943/magento-2-injecting-interfaces