feat: added the setupMiddlewares option (#4068)

Author: snitin315

Diff for: examples/setup-middlewares/README.md

@@ -0,0 +1,49 @@
+# setupMiddlewares
+
+Provides the ability to execute a custom function and apply custom middleware(s).
+
+**webpack.config.js**
+
+```js
+module.exports = {
+  // ...
+  devServer: {
+    setupMiddlewares: (middlewares, devServer) => {
+      if (!devServer) {
+        throw new Error("webpack-dev-server is not defined");
+      }
+
+      devServer.app.get("/setup-middleware/some/path", (_, response) => {
+        response.send("setup-middlewares option GET");
+      });
+
+      middlewares.push({
+        name: "hello-world-test-one",
+        // `path` is optional
+        path: "/foo/bar",
+        middleware: (req, res) => {
+          res.send("Foo Bar!");
+        },
+      });
+
+      middlewares.push((req, res) => {
+        res.send("Hello World!");
+      });
+
+      return middlewares;
+    },
+  },
+};
+```
+
+To run this example use the following command:
+
+```console
+npx webpack serve --open
+```
+
+## What Should Happen
+
+1. The script should open `http://localhost:8080/` in your default browser.
+2. You should see the text on the page itself change to read `Success!`.
+3. Go to `http://localhost:8080/setup-middleware/some/path`, you should see the text on the page itself change to read `setup-middlewares option GET`.

Diff for: examples/setup-middlewares/app.js

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+"use strict";
+
+const target = document.querySelector("#target");
+
+target.classList.add("pass");
+target.innerHTML = "Success!";

Diff for: examples/setup-middlewares/webpack.config.js

@@ -0,0 +1,36 @@
+"use strict";
+
+// our setup function adds behind-the-scenes bits to the config that all of our
+// examples need
+const { setup } = require("../util");
+
+module.exports = setup({
+  context: __dirname,
+  entry: "./app.js",
+  devServer: {
+    setupMiddlewares: (middlewares, devServer) => {
+      if (!devServer) {
+        throw new Error("webpack-dev-server is not defined");
+      }
+
+      devServer.app.get("/setup-middleware/some/path", (_, response) => {
+        response.send("setup-middlewares option GET");
+      });
+
+      middlewares.push({
+        name: "hello-world-test-one",
+        // `path` is optional
+        path: "/foo/bar",
+        middleware: (req, res) => {
+          res.send("Foo Bar!");
+        },
+      });
+
+      middlewares.push((req, res) => {
+        res.send("Hello World!");
+      });
+
+      return middlewares;
+    },
+  },
+});