JavaScript issues that break vendor sites

Vendor sites are typically not built by large engineering teams, and JavaScript issues are common. Here is a rundown of the failures I have encountered and how to work around them.

Photo upload failures

The most frequent JS problem I see is the photo upload widget failing silently. The upload progress bar completes, the page appears to accept the file, and then no preview appears or the file is absent when you reach the order summary. Usually caused by the upload handler hitting an error it does not surface to the user.

Fix: try a different browser. Chrome and Firefox handle JS upload widgets differently. A file that fails in Firefox often succeeds in Chrome, or vice versa. If both fail, try disabling browser extensions one at a time — ad blockers and privacy extensions sometimes block the upload request if the image host is on a blocklist.

Form submission that does nothing

Clicking "Continue" or "Place Order" and nothing happening is a JS error in the form submission handler. Open your browser's developer console (F12, then Console tab) before clicking and watch for red error messages when the button is clicked. Common causes: payment widget not loading because of a content blocker, required field validation that does not surface the error message, or a session timeout that broke the page.

Price calculator not updating

Some vendor sites calculate order totals dynamically as you configure options. If the total stays at $0 or does not change when you add items, the JS calculation function failed. Refresh the page and do not use browser back/forward navigation mid-order — these frequently break JS state on single-page app checkouts.

General approach

Start with a fresh browser window, not a tab that has been open for hours. Clear cookies for the vendor domain if you experience repeated session issues. Use desktop rather than mobile for complex order forms — mobile JS engines handle edge cases differently and some vendor site features simply do not work on mobile.