Nashorn isn&#x27;t actually used in Java&#x27;s WebView (which my project leverages). Nashorn is used elsewhere in the JRE and replaces Rhino from prior releases, but WebView has used something else entirely: JavaScriptCore. Details: <a href="http:&#x2F;&#x2F;stackoverflow.com&#x2F;questions&#x2F;30104124&#x2F;what-javascript-engine-used-inside-javafx&#x2F;30110389#30110389" rel="nofollow">http:&#x2F;&#x2F;stackoverflow.com&#x2F;questions&#x2F;30104124&#x2F;what-javascript-...</a><p>But essentially on performance, it&#x27;s comparable to a desktop browser but still slower than I&#x27;d like. Java 9 should support HTTP 2 and async HTTP by default, which might help. And I&#x27;ve been looking into short-cutting some of the in-memory rendering but haven&#x27;t had any breakthroughs yet.<p>As far as JavaScriptCore engine specifically, it&#x27;s the default in WebKit so there should be good performance data out there on it.