This demo gives GuessJS a route provider with some fake data.
Running this site in development (gridsome develop) should work fine, with the browser console telling you which routes it will prefetch: Prefetching /markdown-test-file, Prefetching /a-post-with-a-cover-image etc.
However, running gridsome build gives the below error:
95% emitting GuessPlugin /path-to-site/guessjs/node_modules/guess-webpack/dist/guess-webpack/main.js:660
compilation.assets[mainName] = new ConcatSource(stats.compilation.assets['./output.js'], '\n', old.source());
^
TypeError: Cannot read property 'source' of undefined