If you’re working with Shopify custom scripts, themes, or third-party integrations, you might encounter the frustrating JavaScript error:

This message often appears in the browser console when trying to override, redefine, or modify Shopify’s built-in JavaScript object.

In this guide, we’ll break down why this happens, what it means, and how to fix it properly — whether you’re editing a Shopify theme, using a headless storefront, or working with an external JavaScript library.

1. Understanding the Error “Cannot Redefine Property”

In JavaScript, a “property” refers to a key-value pair associated with an object. For example:

When you define a property using Object.defineProperty(), JavaScript allows you to set specific rules — such as whether it can be changed or deleted.

The error “Cannot redefine property” occurs when you try to redefine a property that has already been defined as non-configurable.

Example in Plain JavaScript

If you later try to run this:

You’ll get:

Because once a property is defined as non-configurable, it cannot be redefined or modified — not even with the same name.

2. Why It Happens in Shopify

Shopify injects a global “Shopify” object into every storefront’s JavaScript environment. This object includes data like:

This object is often defined by Shopify’s core JavaScript files (for example: shopify_common.js or theme.js).

When a developer, theme, or third-party script tries to overwrite or reassign window.Shopify, it conflicts with the existing definition — triggering the error “Cannot redefine property: Shopify”.

Common Scenarios Where This Error Appears

1. Custom scripts in theme.liquid redefining the Shopify object:

   window.Shopify = {}; // ❌ Causes error


2. App integrations or analytics scripts injecting Shopify again:

   Object.defineProperty(window, 'Shopify', { value: { appData: true } });


3. Bundled JavaScript frameworks (Webpack, React, Vue) that import Shopify objects incorrectly or define them globally.

4. Conflict between two scripts — one loaded by Shopify, another by your custom app — both defining window.Shopify.

3. How to Fix the “Cannot Redefine Property: Shopify” Error

Let’s go through step-by-step methods to identify and fix this issue safely.

Step 1: Inspect Your Console and Script Sources

1. Open your store in Chrome.

2. Press F12 → open the Console tab.

3. Check where the error appears — it should mention a specific file and line number, for example:

   theme.js:452 Uncaught TypeError: Cannot redefine property: Shopify


This helps you locate which script is trying to redefine the Shopify object.

Step 2: Search for Shopify in Your Theme Code

Go to your Shopify admin:

• Online Store → Themes → Edit Code

• Search for window.Shopify or Object.defineProperty(

If you see something like:

replace it with a safe extension method.

Step 3: Use a Safe Extend or Merge Instead of Redefine

You can safely add properties to the existing Shopify object rather than redefining it.

✅ Correct way:

✅ Or using Object.assign():

These methods extend the object without attempting to redefine it.

Step 4: Avoid Object.defineProperty() for Global Objects

If you must define a property, always make it configurable:

Never redefine Shopify’s built-in object directly — use a new name (e.g., ShopifyApp, ShopifyCustom, ShopifyPlus) to avoid conflicts.

Step 5: Check for Conflicting Apps or Scripts

If the error persists:

1. Temporarily disable third-party apps that inject JavaScript.

2. Reload your store and check if the error disappears.

3. Re-enable each app one by one to identify the source.

Common culprits:

• SMS/Popup apps

• Analytics integrations

• Tracking pixels that use window.Shopify data

The “Cannot redefine property: Shopify” error is a classic JavaScript issue caused by trying to overwrite a protected, non-configurable object.

In Shopify, this typically means that a theme, app, or custom script is incorrectly redefining window.Shopify.
The fix is simple — don’t redefine it; extend it.

By following best practices such as:

• Using Object.assign()

• Avoiding global overwrites

• Checking for third-party conflicts

You’ll ensure your Shopify scripts remain stable, scalable, and error-free.

10. FAQ: “Cannot Redefine Property: Shopify”

Q1. Why does this happen only on Shopify pages?

Because Shopify injects a global Shopify object into every storefront page, making it non-configurable. Any redefinition attempt causes the error.

Q2. Can I disable or remove Shopify’s built-in object?

No. It’s part of Shopify’s runtime. Instead, extend it or create your own namespace.

Q3. Does this affect my theme’s functionality?

Yes. Overwriting the Shopify object may break cart updates, AJAX calls, and checkout functions.

Q4. How can I safely add custom data to Shopify?

Use:

Q5. I’m using a third-party app. How do I fix this error?

Contact the app developer — provide the console error and script location. They can update their code to safely merge data instead of redefining.