Shopify.js

import DeliveryMessageHelper from "./Helper";

export default class DeliveryMessageShopify {
    static EVENT_DONE () {
        return 'DeliveryMessageShopify::DONE'
    } 
    
    constructor () {
        this.shop = Shopify.shop
        this.isProductPage = DeliveryMessageShopify.checkProductPage()
        this.isCollection = DeliveryMessageShopify.checkCollection()
        this.productURL = DeliveryMessageShopify.getProductURL()
        this.collectionURL = DeliveryMessageShopify.getCollectionURL()
        this.fetchShopifyData()
    }

    /**
     * Fetch product and collection data from current shop.
     */
    async fetchShopifyData () {
        if (this.isProductPage !== true) {
            return
        }
        try {
            const fetches = []
            fetches.push(this.fetchProduct())
            if (this.isCollection) {
                fetches.push(this.fetchCollection())
            }
            const response = await Promise.all(fetches)
            const shopifyData = {}

            shopifyData.product = response[0]
            if (this.isCollection) {
                shopifyData.collection = response[1].collection
            }

            document.dispatchEvent(
                new CustomEvent(DeliveryMessageShopify.EVENT_DONE(), {
                    detail: shopifyData
                })
            )
        } catch (error) {
            console.log(error)
        }
    }

    /**
     * Fetch product from current store.
     * @returns {Promise}
     */
    fetchProduct () {
        return fetch(this.productURL, {
            credentials: 'same-origin'
        }).then(response => response.json())
    }

    /**
     * Fetch collection from current store.
     * @returns {Promise}
     */
    fetchCollection () {
        return fetch(this.collectionURL, {
            credentials: 'same-origin'
        }).then(response => response.json())
    }

    /**
     * Get myshopify.com URL. 
     * @returns {String}
     */
    static getShop () {
        return Shopify.shop
    }

    /**
     * Check if current page is a product page.
     * @returns {Boolean}
     */
    static checkProductPage () {
        return /products/.test(DeliveryMessageHelper.getCurrentURL()) === true
    }

    /**
     * Check if product page contains an collection.
     * @returns {Boolean}
     */
    static checkCollection () {
        return (DeliveryMessageShopify.checkProductPage() === true) && 
            (/collections/.test(DeliveryMessageHelper.getCurrentURL()) === true)
    }

    /**
     * Get current product API URL.
     * @returns {String}
     */
    static getProductURL () {
        if (DeliveryMessageShopify.checkProductPage() === true) {
            return `${DeliveryMessageHelper.getCurrentURL()}.js`
        }
        return null
    }

    /**
     * Get collection API URL from current product.
     * @returns {String}
     */
    static getCollectionURL () {
        if (DeliveryMessageShopify.checkCollection() === true) {
            const paths = window.location.pathname.split('/')
            return `${window.location.origin}/${paths[1]}/${paths[2]}.json`
        }
        return null
    }
}

Helper class: https://gist.github.com/tobiasdalhof/d54082e56d2ea49408f3d42c5ac59d52