Shopify Functions

1. Concepts

• Deterministic: Same input always equals same output. No random numbers, no network calls.
• Execution Time: Strict limits (e.g., 5ms for logic).
• Languages: Rust (First-class) or JavaScript (via Javy).

2. Structure

1. shopify.extension.toml

   : Configuration.

2. input.graphql

   : Defines data sent to the function.

3. src/run.rs

   (or

   .js

   ): The logic that returns an

   Output

   .

3. Workflow

1. Generate:

   shopify app generate extension --template product_discounts --name my-discount

2. Input Query: Modify

   input.graphql

   to request necessary data (Cart, Customer, etc.).
3. CodeGen: Run

   shopify app function typegen

   to generate types from your GraphQL query.
4. Logic: Implement the

   run

   function.
5. Build:

   npm run build

   (compiles to

   .wasm

   ).
6. Deploy:

   shopify app deploy

   .

4. JS Example (Product Discount)

// src/run.js
// @ts-check

/**
 * @typedef {import("../generated/api").RunInput} RunInput
 * @typedef {import("../generated/api").FunctionRunResult} FunctionRunResult
 */

/**
 * @param {RunInput} input
 * @returns {FunctionRunResult}
 */
export function run(input) {
  const targets = input.cart.lines
    .filter(line => line.merchandise.product.hasAnyTag)
    .map(line => ({
      cartLine: {
        id: line.id
      }
    }));

  if (!targets.length) {
    return {
      discounts: [],
      discountApplicationStrategy: "FIRST",
    };
  }

  return {
    discounts: [
      {
        targets,
        value: {
          percentage: {
            value: "10.0"
          }
        },
        message: "VIP Discount"
      }
    ],
    discountApplicationStrategy: "FIRST",
  };
}

5. Configuration (GraphiQL)

npm run dev