How to Build a Customizable Related Products Section | https://www.shopify.com/partners/blog/related-products

product-reccomendations-script.js

{% javascript %}
var loadProductRecommendationsIntoSection = function() {
  // Look for an element with class 'product-recommendations'
  var productRecommendationsSection = document.querySelector(".product-recommendations");
  if (productRecommendationsSection === null) { return; }
  // Read product id from data attribute
  var productId = productRecommendationsSection.dataset.productId;
  // Read limit from data attribute
  var limit = productRecommendationsSection.dataset.limit;
  // Build request URL
  var requestUrl = "/recommendations/products?section_id=product-recommendations&limit="+limit+"&product_id="+productId;
  // Create request and submit it using Ajax
  var request = new XMLHttpRequest();
  request.open("GET", requestUrl);
  request.onload = function() {
    if (request.status >= 200 && request.status < 300) {
      var container = document.createElement("div");
      container.innerHTML = request.response;
      productRecommendationsSection.parentElement.innerHTML = container.querySelector(".product-recommendations").innerHTML;
    }
  };
  request.send();
};
// If your section has theme settings, the theme editor
// reloads the section as you edit those settings. When that happens, the
// recommendations need to be fetched again.
// See https://help.shopify.com/en/themes/development/sections/integration-with-theme-editor
document.addEventListener("shopify:section:load", function(event) {
  if (event.detail.sectionId === "product-recommendations") {
    loadProductRecommendationsIntoSection();
  }
});
// Fetching the recommendations on page load
loadProductRecommendationsIntoSection();
{% endjavascript %}