Quick answer: If the selected option changes but the price, URL, image, or submitted variant ID does not, the theme’s variant-change JavaScript is failing or outdated. Check console errors and confirm the hidden variant ID updates before adding code.
The real symptom
A customer selects a different size or color, but the visible price stays the same, the URL never updates, or Add to cart submits the default variant.
Likely causes
- JavaScript error stops the variant handler.
- The hidden name=”id” input never changes.
- Picker and form belong to different section instances.
- Custom code removed a theme event.
- Quick add lacks the data needed to update price.
- Theme version has a known variant-picker bug.
- An app duplicated the product form.
Confirmed Community fix
A confirmed Tinker theme case was fixed by updating the theme version, not by layering a new generic script over the broken one. Community cases also identify console errors blocking product scripts.
Exact admin path
- Duplicate the affected theme.
- Check for an available theme update.
- Review release notes for product-form or variant fixes.
- Test the updated draft theme.
- If no update exists, inspect product form and JavaScript in the duplicate.
Simple checks
const productForm = document.querySelector('form[action*="/cart/add"]');
const variantInput = productForm?.querySelector('[name="id"]');
console.log({ formFound: Boolean(productForm), submittedVariantId: variantInput?.value });Run before and after selecting another option. If the ID never changes, the bug occurs before cart submission.
Do not do this
Do not paste a generic variant-price script on top of a modern theme before reading console errors and checking for a theme update.