Add comment explaining what this does

Author: timneutkens

build/webpack/plugins/pages-plugin.js

@@ -8,18 +8,24 @@ import {
 export default class PagesPlugin {
   apply (compiler: any) {
     compiler.hooks.compilation.tap('PagesPlugin', (compilation) => {
+      // This hook is triggered right before a module gets wrapped into it's initializing function,
+      // For example when you look at the source of a bundle you'll see an object holding `'pages/_app.js': function(module, etc, etc)`
+      // This hook triggers right before that code is added and wraps the module into `__NEXT_REGISTER_PAGE` when the module is a page
+      // The reason we're doing this is that we don't want to execute the page code which has potential side effects before switching to a route
       compilation.moduleTemplates.javascript.hooks.render.tap('PagesPluginRenderPageRegister', (moduleSourcePostModule, module, options) => {
         const {chunk} = options
 
-        // check if the current module is the entry module
+        // check if the current module is the entry module, we only want to wrap the topmost module
         if (chunk.entryModule !== module) {
           return moduleSourcePostModule
         }
 
+        // Check if the chunk is a page
         if (!IS_BUNDLED_PAGE_REGEX.test(chunk.name)) {
           return moduleSourcePostModule
         }
 
+        // Match the route the chunk belongs to
         let routeName = ROUTE_NAME_REGEX.exec(chunk.name)[1]
 
         // We need to convert \ into / when we are in windows