Can I truly preview a page prior to publishing it in headless rendering mode?

Apologies in advance for the newbie-level question. According to the Sitecore JSS site ( https://jss.sitecore.com/features ), Sitecore JSS allows you to "preview all your items on your website without publishing them first." That sounds like I can preview an item before publishing but I cannot preview all of the items in the context of a page like I can normally in Sitecore. Is that correct?

Thanks,
Tomer