feat: allow postProcess to return a promise (#243)

* feat: allow postProcess to return a promise

* docs: add async postProcess example

* refactor: undo changes to postProcessHtml

README.md

@@ -281,7 +281,7 @@ In the interest of transparency, there are some use-cases where prerendering mig
 | staticDir | String | Yes | None | The root path to serve your app from. |
 | ouputDir | String | No | None | Where the prerendered pages should be output. If not set, defaults to staticDir. |
 | indexPath | String | No | `staticDir/index.html` | The index file to fall back on for SPAs. |
-| postProcess | Function(Object context): Object | No | None | See the [Using the postProcess Option](#using-the-postprocess-option) section. |
+| postProcess | Function(Object context): [Object \| Promise] | No | None | See the [Using the postProcess Option](#using-the-postprocess-option) section. |
 | minify | Object | No | None | Minifies the resulting HTML using [html-minifier](https://github.com/kangax/html-minifier). Full list of options available [here](https://github.com/kangax/html-minifier#options-quick-reference). |
 | server | Object | No | None | App server configuration options (See below) |
 | renderer | Renderer Instance or Configuration Object | No | `new PuppeteerRenderer()` | The renderer you'd like to use to prerender the app. It's recommended that you specify this, but if not it will default to `@prerenderer/renderer-puppeteer`. |
@@ -296,7 +296,7 @@ In the interest of transparency, there are some use-cases where prerendering mig
 
 #### Using The postProcess Option
 
-The `postProcess(Object context): Object` function in your renderer configuration allows you to adjust the output of `prerender-spa-plugin` before writing it to a file. It is called once per rendered route and is passed a `context` object in the form of:
+The `postProcess(Object context): Object | Promise` function in your renderer configuration allows you to adjust the output of `prerender-spa-plugin` before writing it to a file. It is called once per rendered route and is passed a `context` object in the form of:
 
 ```javascript
 {
@@ -315,7 +315,7 @@ The `postProcess(Object context): Object` function in your renderer configuratio
 
 You can modify `context.html` to change what gets written to the prerendered files and/or modify `context.route` or `context.outputPath` to change the output location.
 
-You are expected to adjust those properties as needed, then return the context object, like so:
+You are expected to adjust those properties as needed, then return the context object, or a promise that resolves to it like so:
 
 ```javascript
 postProcess(context) {
@@ -327,6 +327,14 @@ postProcess(context) {
 
   return context
 }
+
+postProcess(context) {
+  return someAsyncProcessing(context.html)
+    .then((html) => {
+      context.html = html;
+      return context;
+    });
+}
 ```
 
 ---

es5-autogenerated/index.js

@@ -92,9 +92,9 @@ PrerenderSPAPlugin.prototype.apply = function (compiler) {
     })
     // Run postProcess hooks.
     .then(function (renderedRoutes) {
-      return _this2._options.postProcess ? renderedRoutes.map(function (renderedRoute) {
+      return _this2._options.postProcess ? Promise.all(renderedRoutes.map(function (renderedRoute) {
         return _this2._options.postProcess(renderedRoute);
-      }) : renderedRoutes;
+      })) : renderedRoutes;
     })
     // Check to ensure postProcess hooks returned the renderedRoute object properly.
     .then(function (renderedRoutes) {

es6/index.js

@@ -81,7 +81,7 @@ PrerenderSPAPlugin.prototype.apply = function (compiler) {
       )
       // Run postProcess hooks.
       .then(renderedRoutes => this._options.postProcess
-        ? renderedRoutes.map(renderedRoute => this._options.postProcess(renderedRoute))
+        ? Promise.all(renderedRoutes.map(renderedRoute => this._options.postProcess(renderedRoute)))
         : renderedRoutes
       )
       // Check to ensure postProcess hooks returned the renderedRoute object properly.