Exit early from update hooks

When developing Shopify hooks, a common challenge arises from the “updated” events that fire whenever a resource is changed. This means that hooks listening for these events may trigger upon every change, leading to potential issues, particularly recursive cycles if the hooks themselves modify the resource. To mitigate these risks, we recommend two key best practices:

Exit early when the hook has nothing to do
Ensure changes are idempotent by tagging the resource

Practical Example

Consider a scenario where a hook is triggered when a product is updated. The primary goal of this hook is to generate a meta description if it is empty or contains fewer than 150 characters. If the meta description already exists, the hook should exit early to avoid unnecessary processing.

Here’s a simplified implementation demonstrating this pattern:

const TAG_UPDATED_BY = 'updated-by-description-generator';

module.exports = async function (payload, actions, context) {
  try {
    // Check if the meta description has already been generated
    if (payload.tags && payload.tags.includes(TAG_UPDATED_BY)) {
      console.log('This product already has a generated meta description.');
      return; // Exit early
    }

    // Retrieve the current meta description
    let description = await getMetaDescription(payload.id);

    // Generate a new description if it's either absent or too short
    if (!description || description.length <= 150) {
      description = await generateMetaDescription(payload);
    }

    // Save the new description and tag the product to prevent future updates
    await addDescriptionAndTagToProduct(payload.id, description, TAG_UPDATED_BY);
  } catch (err) {
    console.error('Error occurred:', err);
  }
};

Key Takeaways

Early exit: The hook first checks for the existence of a specific tag that indicates whether a meta description has already been generated. If the tag is found, the hook halts immediately, preventing unnecessary updates.
Idempotence: If the description is absent or not up to standard, the hook will generate a new meta description and save it, tagging the product in the process. This ensures that repeated triggers of the hook do not result in redundant operations.

By adhering to these practices, you can enhance the stability and performance of your hooks, while avoiding the pitfalls of unnecessary execution and recursive cycles. Always ensure your hooks are efficient, maintainable, and robust to changes in resource state.