Download websites that use Cart.js

Front-end libraries are copied rather than installed, and copies do not update themselves. Cart.js is a small JavaScript helper released under the MIT license in 2014 to make Shopify's cart endpoints pleasant to work with, so a theme could add an item, change a quantity or redraw a cart drawer without reloading the page. A shop that loads it is unlikely to be running an unmodified stock theme.

The absence of a stock theme is the commercially useful part. Somebody wrote custom cart behavior on that storefront, which means an agency, a freelancer or an in-house developer was paid to work on it, and a merchant willing to pay for theme development is a different prospect from one who picked a template and moved on. The library also dates the work, because a theme built around it reflects the front-end conventions of the period when the library was current.

Version data supports that reading. We separate 5 distinct release strings, a narrow spread for a library of this age, with 1.1.0 as the common reading. A package that has stopped moving leaves its copies frozen wherever they landed, and the thin variation says the dependency was pasted into a theme once and never revisited. For anyone auditing front-end debt across a portfolio of stores, a frozen cart library is a reliable marker of a theme nobody has opened in years.

Detection undercounts here, and the reason matters. Theme builds increasingly bundle and minify their dependencies into a single asset, and a bundled or renamed copy of the library is not something we can attribute with confidence. What we see leans toward stores that still load the file as a separate script, which is itself correlated with older builds. As of October 2026 we record Cart.js on 793 sites, and the honest description of that figure is the visible remainder rather than the true installed base.

A per-domain check confirms one storefront. The list answers what a check cannot: how many custom Shopify themes of that generation are still in production, which markets and top-level domains they sit in, and whose agency work is still running long after the engagement ended. App vendors use the same rows to find stores whose cart is already customized, because a customized cart is where their integration either fits or breaks.