add example for pooling browsers

package.json

@@ -18,6 +18,7 @@
     "cli-table": "^0.3.1",
     "del": "^3.0.0",
     "express": "^4.16.3",
+    "generic-pool": "^3.4.2",
     "lighthouse": "^2.9.4",
     "mime": "^2.3.1",
     "node-fetch": "^2.1.2",

puppeteer-browser-pool.js

@@ -0,0 +1,66 @@
+/**
+ * Copyright 2018 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * @author rahulkumar66@ (Rahul Kumar)
+ */
+
+/**
+* Demonstrates how to reuse browser instances across multiple tasks
+* resulting in improved load times for subsequent requests.
+* This has huge load time improvements in case of SPAs
+*/
+
+const genericPool = require('generic-pool');
+const puppeteer = require('puppeteer');
+
+const VIEWPORT = {width: 1028, height: 800, deviceScaleFactor: 2};
+const HACKER_NEWS_URL = 'https://hn.algolia.com/';
+const HACKER_NEWS_QUERY_URL = `${HACKER_NEWS_URL}?query=chrome`;
+
+const browserPoolFactory = {
+  create: async () => {
+    const browser = await puppeteer.launch({headless: false});
+    const page = await browser.newPage();
+    return page;
+  },
+  destroy: (browser) => {
+    return browser.close();
+  },
+};
+
+const browserPool = genericPool.createPool(browserPoolFactory, {
+  max: 5, // maximum number of browser instances that can be created at any given time 
+  min: 2, // minimum number of browser instances to keep in pool at any given time
+  maxWaitingClients: 50
+});
+
+async function getContent(url) {
+  const page = await browserPool.acquire();
+  await page.setViewport(VIEWPORT);
+
+  const response = await page.goto(url, {waitUntil: 'networkidle2', timeout: 60000});
+  // release browser instance back to pool so it can be reused
+  await browserPool.release(page);
+  return response.text();
+}
+
+(async () => {
+  const responseHackerNews = await getContent(HACKER_NEWS_URL);
+  console.log(responseHackerNews);
+
+  // this request will use the instance from the current browser pool resulting in faster response
+  const responseHackerNewsWithQuery = await getContent(HACKER_NEWS_QUERY_URL);
+  console.log(responseHackerNewsWithQuery);
+})();