In Webpack 4 all modules added using the webpack.PrefetchPlugin also get a reason object explaining why the assets was added. The reason object will have a type: "prefetch" property indicating that the PrefetchPlugin added it, and potentially more reasons if the asset was also required by other modules.
All modules also have a prefetched property indicating whether or not it was prefetched, which we could use instead of checking reasons. But that would also apply to any dynamically required modules using the webpackPrefetch comment hint. Thus to keep the logic as close as possible to how it worked in Webpack 3 this only checks for a Webpack 4's prefetch reason object.
In Webpack 4 all modules added using the
webpack.PrefetchPluginalso get a reason object explaining why the assets was added. The reason object will have atype: "prefetch"property indicating that thePrefetchPluginadded it, and potentially more reasons if the asset was also required by other modules.All modules also have a
prefetchedproperty indicating whether or not it was prefetched, which we could use instead of checkingreasons. But that would also apply to any dynamically required modules using thewebpackPrefetchcomment hint. Thus to keep the logic as close as possible to how it worked in Webpack 3 this only checks for a Webpack 4'sprefetchreason object.