This is an advanced guideline for storefront developers to use Subi Javascript SDK. This SDK primarily renders a subscription widget in the storefront product page, which allows the customers to purchase products with selling plans created by the merchant in the Subi app. This document helps developers to specialize use cases of this subscription widget in their storefront. It includes rendering the widget in unique themes (e.g. headless themes), other pages of the storefront (e.g. landing, collection, or featured products page), and unique components (e.g. quick-buy modal). It further shows how to add event listeners on specific events, e.g. when a selling plan is selected or changed in the widget.