Shopify theme + Vuejs + Custom Elements

This is a 2 part post

• part 1: Idea (current)
• part 2: implementation

Utilizing the power of Web Components it is now possible to create framework-agnostic complex UIs using your favourite JavaScript framework. Recently, I used vue-custom-element to build a Shopify theme. In this article which is my first ever personal blog post, I am going to explain the idea and the challenges I faced implementing it.

Why

That's mainly my personal preference to experience developing with Vuejs and moving the edges of its applications. Turns out you end up with a theme that is more flexible than a conventional Shopify theme.

The idea

Simply put, the idea is to use custom elements in Liquid template files and pass data to them as props and slots. For example, the following would be a custom element that accepts a Liquid object as the orders prop.

<my-orders orders="{{-customer.orders | json-}}"></my-orders>

Liquid is not solid

Shopify uses Liquid files which are like Blade template files if you come from a Laravel world, but the difference is that Blade is designed for developers and Liquid seems to be more end user-oriented resulting in a set of less flexible API.

Here is the minimal snippet to display cart items in templates/cart.liquid file

<table class="responsive-table">
  <thead>
    <tr>
      <th colspan="2">Product</th>
      <th>Price</th>
      <th>Quantity</th>
      <th>Total</th>
    </tr>
  </thead>
  <tbody>
    {% for item in cart.items %}
      <tr >
        <td>
          {% if item.image != blank %}
          <a href="{{ item.url | within: collections.all }}">
            {{ item | img_url: '240x240' | img_tag: item.title }}
          </a>
          {% endif %}
        </td>
        <td>
          <a href="{{ item.url }}">{{ item.product.title }}</a>

          {% unless item.product.has_only_default_variant %}
            <p>{{ item.variant.title }}</p>
          {% endunless %}

          <p>{{ item.vendor }}</p>

          {%- assign property_size = item.properties | size -%}

          {% if property_size > 0 %}
            {% for p in item.properties %}
                {% unless p.last== blank %}
                    {{ p.first }}:
                    {% if p.last contains '/uploads/' %}
                        <a href="{{ p.last }}">{{ p.last | split: '/' | last }}</a>
                    {% else %}
                        {{ p.last }}
                    {% endif %}
                {% endunless %}
            {% endfor %}
        {% endif %}

          <a href="/cart/change?line={{ forloop.index }}&amp;quantity=0">
            <small>Remove</small>
          </a>
        </td>

        <td data-label="{{ 'cart.label.price' | t }}">
            {% if item.original_line_price != item.line_price %}
                {{ item.price | money }} <s>{{ item.original_price | money }}</s>
            {% else %}
                {{ item.price | money }}
            {% endif %}
        </td>

        <td>
          <input
            type="number"
            name="updates[]"
            id="updates_{{ item.key }}"
            value="{{ item.quantity }}"
            min="0"
          />
        </td>

        <td>
          {{ item.line_price | money }}
        </td>
      </tr>

      {% endfor %}
    </td>
  </tbody>
</table>

Boring! I feel like in 2008! Also, it is static, when a user updates the quantity the page reloads, when they remove an item, the page reloads. To add a modern look and feel to it (AKA. better UX) the only way to go for is to add jQuery or JS code to the page that prevents the form submission, communicates to Cart API and manipulate the DOM.

Another thing that I don't appreciate about Liquid is that it encourages to implement the logic alongside the view. That leads to unreadable and hard to maintain code. That is not the case in Balde, since you have the option to abstract away the logic to the controller which is not possible in Shopify.

Custom Element

Using Custom Elements it is possible to move all that into Vuejs to have some fun. In that sense, the templates/cart.liquid would become.

{% if cart.item_count > 0 %}
  <cart-items items:'{{-cart.items | json-}}'></cart-items>
{% else %}
  <p>Cart is empty</p>
{% endif %}

Awesome! Now we can handle it using Vuejs.

Vue Components

The CartItems.vue file can be registered as a Custom Element using the vue-custom-element package.

<template>
  <LineItem v-for="line in cartItems" :key="line.id" :item="line"> </LineItem>
</template>

<script>
  export default {
    props: ["items"],
    data() {
      return {
        cartItems: [],
      };
    },
    created() {
      this.cartItems = parseJson(this.items);
    },
  };
</script>

Here we accept the items as a prop and since it will be a JSON String, we need to use JSON.parse to convert it to an Object.

State Management

It would be nice to keep the cart items as an application state and make it accessible to all other components. Maybe we need to show a counter on the cart icon at the header. It could use our state and that will make it effortlessly reactive. When a user adds an item to the cart. We mutate the cart state and instantly our little counter gets updated.

To do that we can use any state management library like Vuex. We can create a Vuex instance and pass it to all registered Custom elements.

But the problem is that this is not a SPA, Vuex store is an in-memory state, that is, whenever you navigate to another Shopify route the Vuex store data are destroyed. There is a simple solution to that. We can persist state in window.LocalStorage. That way we hydrate the store from LocalStorage when Vuex is loaded.

Aside from reactivity, another benefit to this is that it provides us with a significant little UX improvement. I have noticed many users open PDP pages in New Tab while browsing the product list. Then if you go to a product page and add one to your cart, the other tabs don't have any idea about the state. So, they need to refresh again which is not going to make your UX developer happy.

Now since we are persisting the state, we can also listen to

window.addEventListener('storage', function (event) {...})

and mutate the state. Bingo! all open tabs will get updates if you add a product to the cart.

What is next

In part 2 I will explain the implementation and project structure in more detail.

Originally published at https://ajahandideh.com/shopify-theme-vuejs-custom-elements-part-1-the-idea/