Shopify Checkout UI Extension Development: A Step-by-Step Guide (2026)
This guide scaffolds one from a real Shopify CLI project, reads and writes checkout data through the current shopify global object, tests it locally, and deploys it under the platform's actual constraints. By the end you'll have a working delivery-instructions extension and a clear list of the places these extensions tend to fail once real customers start using them. What You're Building (and What This Guide Skips) The extension in this walkthrough adds a text field to checkout where a customer can leave a note for the courier, and it shows the current order subtotal above the field.
- ▪This guide scaffolds one from a real Shopify CLI project, reads and writes checkout data through the current shopify global object, tests it locally, and deploys it under the platform's actual constraints.
- ▪By the end you'll have a working delivery-instructions extension and a clear list of the places these extensions tend to fail once real customers start using them.
- ▪What You're Building (and What This Guide Skips) The extension in this walkthrough adds a text field to checkout where a customer can leave a note for the courier, and it shows the current order subtotal above the field.
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try { if(localStorage) { let currentUser = localStorage.getItem('current_user'); if (currentUser) { currentUser = JSON.parse(currentUser); if (currentUser.id === 1790752) { document.getElementById('article-show-container').classList.add('current-user-is-article-author'); } } } } catch (e) { console.error(e); } Lucy Posted on Jul 21 Shopify Checkout UI Extension Development: A Step-by-Step Guide (2026) #shopify #webdev #javascript #tutorial Shopify checkout UI extension development means building a small, sandboxed React or Preact component that Shopify renders inside a fixed slot in checkout, such as a block on the Thank you page or a static area next to the cart line items.
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