Developing a product comparison component in Vue.js for 1C-Bitrix

Product Comparison Component Development on Vue.js for 1C-Bitrix

The standard Bitrix comparison component (bitrix:catalog.compare.buy + bitrix:catalog.compare.result) works through page reloads: the user adds a product to the comparison, the page refreshes, the counter changes. The comparison page is a static table. All of this worked in 2010; today UX expectations are different. The Vue.js version: adding to comparison is instant, the header counter updates without a reload, and the comparison table can hide identical characteristics.

Storing the Comparison List

Standard Bitrix stores comparisons in a PHP session ($_SESSION). For the Vue version, localStorage with server synchronization for authenticated users is better — the list persists across sessions and devices.

// stores/compareStore.ts (Pinia)
export const useCompareStore = defineStore('compare', {
    state: () => ({
        items: [] as number[], // product IDs
    }),

    actions: {
        async add(productId: number) {
            if (this.items.includes(productId)) return
            if (this.items.length >= 4) {
                alert('You can compare up to 4 products at once')
                return
            }
            this.items.push(productId)
            localStorage.setItem('compare_items', JSON.stringify(this.items))

            // Sync with server for authenticated users
            if (isLoggedIn()) {
                await fetch('/local/api/compare/add/', {
                    method: 'POST',
                    body: JSON.stringify({ product_id: productId }),
                })
            }
        },

        remove(productId: number) {
            this.items = this.items.filter(id => id !== productId)
            localStorage.setItem('compare_items', JSON.stringify(this.items))
        },

        isInCompare: (state) => (productId: number) => state.items.includes(productId),
    },

    getters: {
        count: (state) => state.items.length,
    },
})

On app initialization the list is loaded from localStorage (for guests) or from the API (for authenticated users, with cross-device merge).

"Compare" Button on the Product Card

<!-- CompareButton.vue -->
<template>
  <button
    :class="['compare-btn', { 'compare-btn--active': isAdded }]"
    @click="toggle"
    :title="isAdded ? 'Remove from comparison' : 'Add to comparison'"
  >
    <IconScale :filled="isAdded" />
    <span>{{ isAdded ? 'In comparison' : 'Compare' }}</span>
  </button>
</template>

<script setup lang="ts">
const props = defineProps<{ productId: number }>()
const store = useCompareStore()
const isAdded = computed(() => store.isInCompare(props.productId))

function toggle() {
    isAdded.value ? store.remove(props.productId) : store.add(props.productId)
}
</script>

The button is mounted on each product card. In the Bitrix template:

// In the product card template.php
?>
<div data-compare-btn data-product-id="<?= $arItem['ID'] ?>"></div>
<?php
// After page load Vue mounts CompareButton into each [data-compare-btn]

Counter in the Site Header

<!-- CompareCounter.vue (mounted in header) -->
<template>
  <a href="/compare/" class="header-compare">
    <IconScale />
    <span class="badge" v-if="count > 0">{{ count }}</span>
  </a>
</template>

<script setup lang="ts">
const store = useCompareStore()
const count = computed(() => store.count)
</script>

The counter updates reactively via Pinia — no global EventBus or DOM manipulation.

Comparison Page

The most complex part — the comparison table. Product data is loaded from the server by ID list:

// In CompareTable.vue
async function loadCompareData(ids: number[]) {
    const res  = await fetch(`/local/api/compare/?ids=${ids.join(',')}`)
    const data = await res.json() // [{id, name, price, specs: {...}}, ...]
    products.value = data
    buildDiffMap()
}

// Identify identical characteristics for the option to hide them
function buildDiffMap() {
    const allSpecs = new Set(products.value.flatMap(p => Object.keys(p.specs)))
    diffMap.value  = {}

    allSpecs.forEach(spec => {
        const values = products.value.map(p => p.specs[spec])
        diffMap.value[spec] = new Set(values).size > 1 // true = there are differences
    })
}

"Show only differences" filter — a button that hides rows where all values are identical:

<template>
  <table class="compare-table">
    <thead>
      <tr>
        <th>Characteristic</th>
        <th v-for="p in products" :key="p.id">
          <ProductCard :product="p" @remove="store.remove(p.id)" />
        </th>
      </tr>
    </thead>
    <tbody>
      <tr
        v-for="spec in visibleSpecs"
        :key="spec"
        :class="{ 'row--different': diffMap[spec] }"
      >
        <td class="spec-name">{{ specLabels[spec] }}</td>
        <td v-for="p in products" :key="p.id">{{ p.specs[spec] ?? '—' }}</td>
      </tr>
    </tbody>
  </table>
</template>

<script setup lang="ts">
const showOnlyDiff = ref(false)
const visibleSpecs = computed(() =>
    showOnlyDiff.value
        ? Object.keys(diffMap.value).filter(k => diffMap.value[k])
        : Object.keys(diffMap.value)
)
</script>

PHP Data Controller for Comparison

// CompareController.php
public function getAction(string $ids): array {
    $idArr = array_filter(array_map('intval', explode(',', $ids)));
    if (!$idArr) return [];

    $products = [];
    $res = CIBlockElement::GetList(
        [],
        ['ID' => $idArr, 'IBLOCK_ID' => CATALOG_IBLOCK_ID, 'ACTIVE' => 'Y'],
        false, false,
        ['ID', 'NAME', 'PREVIEW_PICTURE', 'DETAIL_PAGE_URL', 'CATALOG_PRICE_1_']
    );

    while ($el = $res->GetNext()) {
        // Get properties for comparison
        $props = [];
        $prRes = CIBlockElement::GetProperty(CATALOG_IBLOCK_ID, $el['ID'], [], ['COMPARE' => 'Y']);
        while ($pr = $prRes->Fetch()) {
            $props[$pr['CODE']] = $pr['VALUE'];
        }
        $products[] = [
            'id'    => $el['ID'],
            'name'  => $el['NAME'],
            'price' => $el['CATALOG_PRICE_1_'],
            'image' => $el['PREVIEW_PICTURE'] ? CFile::GetPath($el['PREVIEW_PICTURE']) : null,
            'url'   => $el['DETAIL_PAGE_URL'],
            'specs' => $props,
        ];
    }

    return $products;
}

Properties participating in comparison are flagged with COMPARE = 'Y' in the infoblock settings — a standard Bitrix mechanism.

Fixed First Column on Mobile

The comparison table on mobile is horizontally scrollable. The first column (characteristic names) must be sticky:

.compare-table {
    display: grid;
    grid-template-columns: 180px repeat(4, 1fr);
    overflow-x: auto;
}

.compare-table td:first-child,
.compare-table th:first-child {
    position: sticky;
    left: 0;
    background: white;
    z-index: 1;
}

CSS Grid with position: sticky is a more reliable approach than display: table with fixed columns.

Timeline

Product comparison is a tool for buyers choosing between similar items. A properly implemented comparison helps make a decision on the site rather than leaving for an aggregator.