fix(contribute): fix webpack 4 patterns in plugin-patterns Changed chunks section

Author: raj-sapalya

src/content/contribute/plugin-patterns.mdx

@@ -93,7 +93,13 @@ W> Since webpack 5, `compilation.fileDependencies`, `compilation.contextDependen
 
 ## Changed chunks
 
-Similar to the watch graph, you can monitor changed chunks (or modules, for that matter) within a compilation by tracking their hashes.
+Similar to the watch graph, you can monitor changed chunks within a compilation by tracking their content hashes.
+
+W> In webpack 5, `compilation.chunks` is a `Set`, not an array.
+Calling `.filter()` or `.map()` directly on it throws a `TypeError`.
+Use `for...of` or spread it into an array first.
+
+W> `chunk.hash` was removed in webpack 5. Use `chunk.contentHash.javascript` instead. Using the old property returns `undefined`, causing every chunk to appear changed on every rebuild.
 
 ```js
 class MyPlugin {
@@ -103,15 +109,36 @@ class MyPlugin {
 
   apply(compiler) {
     compiler.hooks.emit.tapAsync("MyPlugin", (compilation, callback) => {
-      const changedChunks = compilation.chunks.filter((chunk) => {
-        const oldVersion = this.chunkVersions[chunk.name];
-        this.chunkVersions[chunk.name] = chunk.hash;
-        return chunk.hash !== oldVersion;
-      });
+      const changedChunks = [];
+
+      for (const chunk of compilation.chunks) {
+        const key = chunk.id ?? chunk.name;
+        const currentHash = chunk.contentHash.javascript;
+
+        if (currentHash === undefined) continue;
+
+        const oldHash = this.chunkVersions[key];
+        this.chunkVersions[key] = currentHash;
+
+        if (currentHash !== oldHash) {
+          changedChunks.push(chunk);
+        }
+      }
+
+      if (changedChunks.length > 0) {
+        console.log(
+          "Changed chunks:",
+          changedChunks.map((chunk) => chunk.id),
+        );
+      }
+
       callback();
     });
   }
 }
 
 export default MyPlugin;
 ```
+
+T> Use `chunk.id ?? chunk.name` as the tracking key. Some chunks have an `id` but no `name`, so relying on `chunk.name` alone can miss changes.
+CSS or other non-JS chunks may not have a `javascript` key in `contentHash` — the `continue` guard skips those safely.