A minor, yet important, react4xp update: lib-react4xp 1.7.1 fixes a bug where the nashorn SSR engine could fail to initialize in XP 7.7 and produce the following server log error message:
ERROR c.e.l.r.ssr.ServerSideRenderer - com.enonic.lib.react4xp.ssr.errors.RenderException: Couldn't init Renderer (#1 etc)
com.enonic.lib.react4xp.ssr.errors.RenderException: Couldn't init Renderer (#1 etc)
at com.enonic.lib.react4xp.ssr.pool.Renderer.<init>(Renderer.java:68)
at com.enonic.lib.react4xp.ssr.pool.RendererFactory.makeObject(RendererFactory.java:31)
...
Caused by: java.lang.NullPointerException
at com.enonic.lib.react4xp.ssr.pool.Renderer.evalAndGetByKey(Renderer.java:117)
at com.enonic.lib.react4xp.ssr.engineFactory.EngineFactory.buildEngine(EngineFactory.java:102)
at com.enonic.lib.react4xp.ssr.pool.Renderer.<init>(Renderer.java:51)
... 143 more
Update lib-react4xp if you upgrade to XP 7.7+.