Shopify Scripts to Functions Migration Guide 2026

The Clock Is Ticking: Why Your Shopify Scripts Migration Cannot Wait

Shopify Scripts will stop running on June 30, 2026. That is not a soft deprecation or a gentle nudge. Every line item script, shipping script, and payment script you have relied on for custom checkout logic will cease to execute. And here is the part most merchants are missing: starting April 15, 2026, you will no longer be able to edit or publish any Shopify Scripts. That means your window to test changes side-by-side is shrinking fast.

If your Shopify Plus store uses Scripts for tiered discounts, free shipping thresholds, payment gateway filtering, or any custom checkout behavior, this shopify scripts to functions migration guide 2026 is your action plan. Thousands of Shopify Plus merchants are in the same position, and the ones who migrate early will avoid the last-minute scramble that crashes developer availability in May and June.

The replacement is Shopify Functions -- a faster, more flexible, and more powerful system built on WebAssembly. Functions execute in under 5 milliseconds (roughly 100x faster than Scripts), support multiple programming languages, and are available to all Shopify plans through public apps. The migration is not optional, but the upside is real.

Understanding What Changes: Scripts vs Functions Architecture

Before you start migrating, you need to understand what is fundamentally different between the two systems. This is not a simple syntax swap.

How Shopify Scripts Worked

Scripts were sandboxed Ruby snippets that ran inside Shopify's checkout pipeline. You wrote them in a proprietary editor, they executed server-side against cart data, and they could modify line item prices, filter shipping rates, and reorder payment gateways. The system was simple but limited -- tied to Ruby, confined to Plus merchants, and increasingly difficult for Shopify to scale.

How Shopify Functions Work

Shopify Functions are compiled WebAssembly (Wasm) binaries that execute on Shopify's core infrastructure. You write them in Rust, JavaScript, or TypeScript (anything that compiles to Wasm), package them inside a Shopify app, and deploy through the Shopify CLI. Functions receive structured input via GraphQL, return structured output, and run in a tightly sandboxed environment with strict performance budgets.

Key Architectural Differences

Functions are not just a replacement -- they are an upgrade. According to Shopify's engineering blog on JavaScript in WebAssembly, JavaScript-compiled Wasm modules run about 3x slower than Rust-compiled ones, but both comfortably finish under the 5ms budget for realistic use cases.

Step 1: Audit Every Active Script in Your Store

The first phase of any shopify scripts to functions migration guide 2026 is a complete audit. You cannot migrate what you do not understand.

Use the Shopify Scripts Customizations Report

Shopify has released an AI-powered customizations report directly in your admin panel. According to the Shopify Changelog announcement, this report displays every active Script customization in your store and provides:

• The name, description, and source file of each Script
• Recommended replacement apps that use Shopify Functions
• Links to relevant Shopify Functions API documentation and tutorials
• Categorized sections for payment, shipping, and discount customizations

Navigate to Settings > Checkout > Scripts in your Shopify admin to access this report.

Document Your Script Logic Manually

Do not rely solely on the automated report. For each active Script, document:

• The business rule it enforces (e.g., "Buy 3 get 10% off all items")
• The trigger conditions (customer tags, cart total, product collections)
• The expected output (price changes, rate filtering, gateway reordering)
• Edge cases you have discovered over time (multi-currency, draft orders, B2B pricing)

Categorize by Migration Complexity

Sort your scripts into three buckets:

Step 2: Map Scripts to Shopify Functions API Types

Each Script category maps to a specific Functions API. Understanding this mapping is critical for planning your rebuild.

Line Item Scripts to Discount Functions

Line Item Scripts that modified cart prices map to the Discount Function APIs. There are three discount types:

• Product Discount API -- applies discounts to specific products or variants in the cart
• Order Discount API -- applies discounts to all merchandise in the cart
• Shipping Discount -- applies discounts to delivery rates via DeliveryDiscountCandidateTarget

You can activate a maximum of 25 discount functions per store, which is more than enough for most merchants but something to plan around if you had dozens of overlapping Scripts.

Shipping Scripts to Delivery Customization Functions

Shipping Scripts that filtered, renamed, or reordered delivery options map to the Delivery Customization Function API. This API lets you:

• Hide specific shipping rates based on cart contents or customer attributes
• Rename delivery options dynamically (e.g., "Standard" becomes "Free 5-7 Day Shipping" above $100)
• Reorder rates to promote preferred carriers

Payment Scripts to Payment Customization Functions

Payment Scripts map to the Payment Customization Function API. You can:

• Hide payment methods based on cart total, customer tags, or product types
• Rename payment gateways for clarity
• Reorder payment options to prioritize preferred methods

One critical difference: execution order has changed. Line Item Scripts ran before Functions, while Shipping and Payment Scripts ran after Functions. If you are running both systems during your transition period, factor this ordering into your testing.

Step 3: Choose Your Migration Path

You have three paths available, and the right one depends on your technical resources and timeline. The Shopify help center's official migration guide outlines each approach.

Path A: Install a Ready-Made App

For simple to moderate Scripts, a pre-built app from the Shopify App Store may cover your needs completely. Apps like SupaEasy: AI Functions Creator use AI to analyze your existing Scripts and generate equivalent Functions code without requiring you to write a single line.

Best for: Merchants without dedicated developers, straightforward discount and shipping rules, fast timelines.

Path B: Build Custom Functions with Shopify CLI

For complex or highly customized logic, building your own Functions app gives you full control. Shopify CLI scaffolds the project structure, and you can write in JavaScript/TypeScript (more accessible) or Rust (more performant).

Best for: Stores with a development team, unique business logic, and the need for precise control over checkout behavior. If you use Shopify Flow for automation, custom Functions integrate cleanly into your existing workflow triggers.

Path C: Hire a Shopify Expert

If your scripts are complex and your team lacks Wasm experience, hiring a specialist is the pragmatic choice. Check the Shopify experts network for developers experienced with Functions migration.

Best for: Stores with critical, revenue-impacting Scripts, limited internal dev resources, or tight timelines approaching the April 15 edit freeze.

Step 4: Build Your First Shopify Function

If you are taking Path B, here is the concrete process for building a discount Function using JavaScript. This example creates a "Buy 3+, get 15% off" volume discount.

Scaffold the Project

shopify app generate extension --template discount --language javascript

This creates the boilerplate structure with the correct Wasm compilation pipeline, GraphQL input queries, and extension configuration files. Shopify CLI uses ESBuild for preprocessing and Javy for Wasm compilation, so you can import npm dependencies normally.

Define the Input Query

Your Function needs to declare what data it requires from the cart. In input.graphql:

query Input {
  cart {
    lines {
      quantity
      merchandise {
        ... on ProductVariant {
          id
          product {
            id
            hasAnyTag(tags: ["volume-discount"])
          }
        }
      }
    }
  }
}

Write the Function Logic

In src/index.js, implement the discount logic:

export function run(input) {
  const MINIMUM_QUANTITY = 3;
  const DISCOUNT_PERCENTAGE = 15.0;

  const targets = input.cart.lines
    .filter(line =>
      line.quantity >= MINIMUM_QUANTITY &&
      line.merchandise?.product?.hasAnyTag
    )
    .map(line => ({
      productVariant: { id: line.merchandise.id }
    }));

  if (targets.length === 0) {
    return { discountApplicationStrategy: "FIRST", discounts: [] };
  }

  return {
    discountApplicationStrategy: "FIRST",
    discounts: [{
      value: { percentage: { value: DISCOUNT_PERCENTAGE.toString() } },
      targets,
      message: "Volume discount: 15% off when you buy 3+"
    }]
  };
}

Test Locally

Run the function against sample input:

shopify app function run --input sample-input.json

Write unit tests that cover your edge cases -- multi-currency carts, zero-quantity lines, mixed eligible and ineligible products. The Shopify function-examples repository on GitHub provides test patterns for every API type.

Step 5: Run Scripts and Functions Side by Side

This is the safety net that makes migration manageable. Scripts and Functions can coexist on the same store until June 30, 2026. Use this to your advantage.

Parallel Testing Strategy

1. Deploy your new Function to a development store or staging environment first
2. Enable both the existing Script and the new Function on your production store
3. Monitor checkout behavior for 1-2 weeks, comparing outcomes
4. Disable the Script once you have confirmed parity
5. Remove the Script entirely before the April 15 edit freeze

Watch for Execution Order Conflicts

Remember the execution order difference:

• Line Item Scripts execute before Discount Functions
• Shipping Scripts execute after Delivery Customization Functions
• Payment Scripts execute after Payment Customization Functions

This means if you have both a Line Item Script and a Discount Function active simultaneously, the Script applies first and the Function sees the already-modified prices. Plan your overlap period carefully to avoid double-discounting.

Validate with Real Orders

Do not rely solely on preview mode. Place real test orders (you can void them immediately) across these scenarios:

• Single-item and multi-item carts
• Guest checkout and logged-in customers
• Desktop and mobile checkout flows
• Multiple shipping addresses (if applicable)
• B2B and DTC customers (if you sell wholesale)

Common Mistakes to Avoid During Migration

Migrations under deadline pressure breed shortcuts. Here are the pitfalls that catch merchants every cycle.

Waiting Until May or June

Developer availability craters as the deadline approaches. Shopify agencies report booking out 4-8 weeks in advance of major deprecation dates. If you are reading this in March 2026, start now. The April 15 edit freeze is three weeks away.

Skipping the Audit Phase

Merchants frequently discover "forgotten" Scripts running logic they did not know existed. A payment Script hiding COD for international orders, a line item Script applying a legacy loyalty discount -- these surface only when they break. Audit thoroughly.

Assuming 1:1 Feature Parity

Some Script behaviors do not have direct equivalents in Functions yet. For example, Scripts could access and modify the presentment_currency directly, while Functions handle multi-currency through Shopify Markets. Shopify's official migration documentation notes specific gaps and workarounds.

Ignoring the 5ms Execution Limit

Functions must complete in under 5 milliseconds. If your Script had complex nested loops iterating over large carts (100+ line items with variant lookups), you may need to optimize your Function logic or switch from JavaScript to Rust. Shopify recommends Rust for stores with consistently large carts.

Not Testing Multi-Currency and B2B Scenarios

If your store operates across multiple markets or has a B2B wholesale channel, test those flows explicitly. Currency conversion, company-specific pricing, and net payment terms all interact with discount and payment Functions in ways that differ from the old Scripts environment.

Migration Timeline: Your Week-by-Week Action Plan

With the April 15 edit freeze and June 30 sunset firmly in place, here is a realistic timeline assuming you start today.

Weeks 1-2: Audit and Plan (Late March 2026)

• Run the Shopify Scripts customizations report
• Document every active Script's business logic
• Categorize by complexity (simple, moderate, complex)
• Decide migration path for each Script (app, custom build, expert)
• If hiring, engage developers now -- not in April

Weeks 3-4: Build and Test (Early April 2026)

• Install replacement apps or scaffold custom Functions
• Deploy to a development store for initial testing
• Write automated tests for each Function
• Compare Function output against Script output for identical inputs

Week 5: Parallel Production Run (Mid-April 2026)

• Deploy Functions to production alongside Scripts
• Note: After April 15, you cannot edit Scripts, so finalize any Script changes before this date
• Monitor checkout conversion rates, average order values, and error logs daily

Week 6: Script Retirement (Late April 2026)

• Disable Scripts one at a time, starting with the simplest
• Verify each retirement does not impact checkout behavior
• Document the completed migration for your team

Weeks 7-12: Buffer (May-June 2026)

• Address any edge cases that surface in production
• Optimize Function performance if needed
• Prepare for June 30 when all remaining Scripts stop automatically

Tools and Resources for a Smooth Migration

You do not have to navigate this alone. The ecosystem has rallied around this deadline.

Official Shopify Resources

• Migrating from Shopify Scripts to Shopify Functions -- the official developer documentation
• Shopify Functions API reference -- complete API documentation for all Function types
• Shopify CLI -- scaffolding, building, testing, and deploying Functions

Third-Party Migration Tools

• SupaEasy: AI Functions Creator -- AI-powered code generation that translates Script logic to Functions
• ScriptShift -- automated Script analysis with migration-ready code output

Community Support

The Talk Shop community hosts active discussions on migration strategies, and our Shopify development resources cover the technical foundations you need. For real-time help from developers who have already migrated, the community Discord is invaluable.

What Happens After June 30: The Functions-First Future

Migration is not just about survival -- it is about positioning your store for what comes next.

Expanded Function Types

Shopify continues to ship new Function APIs. The 2026-04 GraphQL API version added the ability for Functions to access discount details at cart, line item, and delivery levels when they execute after discounts are applied. Expect more API surface area throughout 2026 and beyond.

Performance Gains

Stores that have migrated report measurably faster checkouts. The sub-5ms execution time means your custom logic adds virtually zero latency to the checkout flow. For conversion optimization, every millisecond matters.

App Ecosystem Growth

Because Functions are available to all Shopify plans (not just Plus), the app ecosystem is building aggressively on this platform. More apps, more templates, more community-contributed examples. Your investment in learning Functions pays compounding returns.

Your Migration Starts Today

The shopify scripts to functions migration guide 2026 boils down to this: audit now, build in April, run parallel before the edit freeze, and retire Scripts well before June 30. The stores that treat this as a Q2 project will be scrambling. The stores that start this week will be done before the April 15 lockout even hits.

If you are evaluating whether Shopify Plus is still the right plan for your growing store, our guide on how much Shopify costs per month breaks down the full pricing picture, including how Functions change the value equation.

Run your customizations report today. Pick your migration path. Use our ecommerce tools to audit your store's current setup, and get your checkout logic off a platform that is three months from disappearing.

**What Scripts are you most concerned about migrating? Drop into the Talk Shop community and share your migration plan -- our developers are helping merchants through this transition every day.**

About Talk Shop

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