Shopify Function Tags not Applying

Technical Q&A
,

Topic summary

Issue: A Shopify Function discount isn’t applying at checkout when relying on product tags.

Key logic in Run.js:

  • Filters cart lines with quantity ≥ 2, then checks line.merchandise.product.tags for discount tags.
  • Tag checks are inconsistent: filter looks for “2FOR250” but discount logic checks “2FOR200”, “2FOR300”, and “3FOR500”. There’s also a typo (“p roductTags”).
  • discountValue is computed based on tags/quantity but is never used; the returned discount always applies a fixed 10%.
  • Targets are generated per eligible group but all point to the same cart line ID.

GraphQL input:

  • The query requests product.hasTags only for [“2FOR250”], not for “2FOR200”, “2FOR300”, or “3FOR500”. The function code expects product.tags (an array), which isn’t queried; only hasTags is available.

Outcome/Status:

  • Discounts do not apply at checkout. No resolution or final fix provided.

Notes:

  • Code snippets are central to understanding the problem (Run.js and the RunInput GraphQL query).
Summarized with AI on December 16. AI used: gpt-5.
1 
//Run.js 

// @ts-check
import { DiscountApplicationStrategy } from "../generated/api";

// Use JSDoc annotations for type safety
/**
 * @typedef {import("../generated/api").RunInput} RunInput
 * @typedef {import("../generated/api").FunctionRunResult} FunctionRunResult
 * @typedef {import("../generated/api").Target} Target
 * @typedef {import("../generated/api").ProductVariant} ProductVariant
 */

/**
 * @type {FunctionRunResult}
 */
const EMPTY_DISCOUNT = {
  discountApplicationStrategy: DiscountApplicationStrategy.First,
  discounts: [],
};

/**
 * @param {RunInput} input
 * @returns {FunctionRunResult}
 */
export function run(input) {
  const targets = input.cart.lines
    // Only include cart lines with at least one pair of items (quantity >= 2)
    .filter((line) => line.quantity >= 2)
    // Check for the relevant product tags in the product associated with each cart line
    .filter((line) => {
      // Assuming the tags are part of the product or product variant
      const productTags = line.merchandise.product.tags || [];

      // Check for different discount tags (2FOR200, 2FOR300, 3FOR500)
      const has2FOR200 = productTags.includes("2FOR250");
      const has2FOR300 = productTags.includes("2FOR300");
      const has3FOR500 = productTags.includes("3FOR500");

      // Only include lines with at least one of the discount tags
      return has2FOR200 || has2FOR300 || has3FOR500;
    })
    .map((line) => {
      // Get the appropriate discount based on the tag and quantity
      const productTags = line.merchandise.product.tags || [];
      let discountValue = 0;

      if (productTags.includes("2FOR200") && line.quantity % 2 === 0) {
        discountValue = 16.0; // 16% discount for 2FOR200
      } else if (productTags.includes("2FOR300") && line.quantity % 2 === 0) {
        discountValue = 30.0; // 30% discount for 2FOR300
      } else if (productTags.includes("3FOR500") && line.quantity % 3 === 0) {
        discountValue = 20.0; // 20% discount for 3FOR500
      }

      // Calculate how many groups (pairs or triplets) are eligible for discount
      const eligibleGroups = discountValue > 0 ? Math.floor(line.quantity / (productTags.includes("3FOR500") ? 3 : 2)) : 0;

      // Generate discount targets for each eligible group
      return Array.from({ length: eligibleGroups }, () => /** @type {Target} */ ({
        cartLine: {
          id: line.id,
        },
      }));
    })
    // Flatten the array of arrays into a single array
    .flat();

  // If no targets are found, return empty discount
  if (!targets.length) {
    console.error("No cart lines qualify for the discount.");
    return EMPTY_DISCOUNT;
  }

  return {
    discounts: [
      {
        // Apply the discount to the collected targets
        targets,
        // Define a percentage-based discount (adjust the value dynamically)
        value: {
          percentage: {
            value: "10.0", // Default discount (you can adjust this based on actual logic)
          },
        },
      },
    ],
    discountApplicationStrategy: DiscountApplicationStrategy.First,
  };
}

query RunInput {
  cart{
    lines {     
      quantity
      merchandise {
        ... on ProductVariant {
          product{
            id
            hasTags (tags: ["2FOR250"]) {
              hasTag
              tag
              
            }
          }
          
        }
      }
    }
  }
}

I am having a problem with this code.It is not applying on the tags on checkout.