get-preview-url.js

const domain = await fetch(`https://${config.store}/admin/api/2020-07/shop.json?fields=domain`, {
			method: "GET",
			headers: {
				'X-Shopify-Access-Token': config.password,
				'Content-Type': 'application/json',
				mode: 'cors',
				cache: 'no-cache',
				credentials: 'same-origin',
				redirect: 'follow',
				referrerPolicy: 'no-referrer',
			}
		}).then(response => response.json()).then(response => response.shop.domain);

		let original_preview_url = `https://${domain ? domain : config.store}/?preview_theme_id=${config["theme_id"]}`;;

		let cookies = await fetch(original_preview_url, {
			method: 'GET',
			redirect: 'follow',
		}).then(response => response.headers.get("set-cookie"));

		const preview_bar_url = `https://${domain ? domain : config.store}/preview_bar?preview_theme_id=${config["theme_id"]}`;
		let preview_url = (await axios({
			method: 'get',
			url: preview_bar_url,
			responseType: "html",
			headers: {
				Cookie: cookies
			}
		}).then(response => response.data).then(html => html.match(/(https:|http:)\/\/[\w\-\d]+\.shopifypreview\.com/gm))).shift();