Diffbot does execute JavaScript - it renders in a stripped-down Chrome - but there is a catch in the Article API: individual calls do NOT run JS, only bulk API and Crawlbot calls do. If your single Article API call returns thin content on a JS-rendered page, that is why. Route it through the bulk or crawl path and the same URL comes back with the rendered content.

Context: Stack Overflow (Does Diffbot execute JavaScript?, answered): Yes, Diffbot renders pages in a stripped-down session-less Chrome and visually inspects the result rather than just parsing source. But the Article API does NOT execute JavaScript in individual calls - only in bulk API calls and Crawlbot calls. Single Article API calls on JS-heavy pages return what the static parse sees.