Track every single product and checkout by linking your Google Analytics account with Commerce.js.
Add your Google Analytics tracking ID under Settings > Merchant

Google Analytics
To find the tracking ID and code snippet in Google Analytics:
Sign in to your Analytics account.
Click Admin.
Select an account from the menu in the ACCOUNT column.
Select a property from the menu in the PROPERTY column.
Under PROPERTY, click Tracking Info > Tracking Code. Your tracking ID displayed at the top of the page.