Script to automatically generate service worker after a GWT build and before packaging the app.

package.json

{
  "name": "gwt-pwa",
  "version": "0.0.1",
  "description": "generates service worker for GWT app",
  "main": "serviceWorkerBuilder.js",
  "dependencies": {
    "handlebars": "^4.0.11"
  },
  "devDependencies": {},
  "scripts": {
    "generate": "node serviceWorkerBuilder.js"
  },
  "repository": {
    "type": "git",
    "url": "git+https://github.com/zak905/gwt-pwa-demo.git"
  },
  "author": "zakaria amine",
  "license": "ISC",
  "bugs": {
    "url": "https://github.com/zak905/gwt-pwa-demo/issues"
  },
  "homepage": "https://github.com/zak905/gwt-pwa-demo#readme"
}

pom.xml

<plugin>
	 <groupId>com.github.eirslett</groupId>
        <artifactId>frontend-maven-plugin</artifactId>
        <version>1.6</version>
		<executions>
			<execution>
				<id>npm install</id>
				<goals>
					<goal>npm</goal>
				</goals>
				<phase>generate-resources</phase>
				<configuration>
					<arguments>install</arguments>
				</configuration>
			</execution>
			<execution>
				<id>npm generate</id>
				<goals>
					<goal>npm</goal>
				</goals>
				<phase>prepare-package</phase>
				<configuration>
					<arguments>run-script generate ${project.build.finalName}</arguments>
				</configuration>
			</execution>
		</executions>
	</plugin>

serviceWorkerBuilder.js

const args = process.argv;
const arguments = args.slice(2);

const buildFolderName = arguments[0];
const gwtModuleName = arguments[1];

if (typeof buildFolderName === 'undefined' || !buildFolderName){
    console.log("please provide the name of the build folder");
    return;
}

const rootFolder = 'target/' + buildFolderName;
const fs = require('fs');
var Handlebars = require('handlebars');

var filesToCache = [];


browseAllFilesInDirectory(rootFolder);

function browseAllFilesInDirectory(folder) {
    const filesRegExp = /\.(html|css|js|gif|png|jpeg)$/i;
    const exceptions = ["WEB-INF", "META-INF", "bower_components", "clear.cache.gif"];

    fs.readdirSync(folder).forEach(fileName => {
        const resource = folder + "/" + fileName;
          if (exceptions.indexOf(fileName) < 0) {        
            if (fileName.match(filesRegExp)) {
                    filesToCache.push(resource.replace(rootFolder+"/", ""));
            } else if (fs.lstatSync(resource).isDirectory()) {
                    browseAllFilesInDirectory(resource);
            }
          } 
    });
}

var swData = {
    cacheName: gwtModuleName || "cache_"+new Date().getTime().toString(),
    filesToCache: filesToCache,
};

fs.readFile("sw_template.js", "utf8", (error, data) => {
    if (error) {
       console.log("Unable to read template file");
    }
    var template = Handlebars.compile(data);
   var serviceWorkerJs = template(swData);

   fs.writeFile(rootFolder+"/sw.js", serviceWorkerJs, (error) => {
     console.log("successfully generated service worker sw.js in " + rootFolder);
   });
});

sw_template.js

var cacheName = '{{cacheName}}';  
var filesToCache = [  {{#each filesToCache}}
                     '{{.}}'{{#unless @last}},{{/unless}}
                      {{/each}}
                     ];


self.addEventListener('install', function(e) {  
  console.log('[ServiceWorker] Install');  
  e.waitUntil(  
    caches.open(cacheName).then(function(cache) {  
      console.log('[ServiceWorker] Caching app shell');  
      return cache.addAll(filesToCache);  
    })  
  );  
});


self.addEventListener('activate', function(e) {  
    console.log('[ServiceWorker] Activate');  
    e.waitUntil(  
      caches.keys().then(function(keyList) {  
        return Promise.all(keyList.map(function(key) {  
          console.log('[ServiceWorker] Removing old cache', key);  
          if (key !== cacheName) {  
            return caches.delete(key);  
          }  
        }));  
      })  
    );  
  });

self.addEventListener('fetch', function(e) {  
    console.log('[ServiceWorker] Fetch', e.request.url);  
    e.respondWith(  
      caches.match(e.request).then(function(response) {  
        return response || fetch(e.request);  
      })  
    );  
  });

Hey there this is great but I have some issue on the code itself.

Also when trying to install my app I got this issue.

[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 01:17 min
[INFO] Finished at: 2017-11-06T17:29:46+08:00
[INFO] Final Memory: 29M/501M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal com.github.eirslett:frontend-maven-plugin:1.6:npm (npm install) on project gwt-material-demo: Failed to run task: 'npm install' failed. java.io.IOException: Cannot run program "/home/mark/Documents/github/gwt-material-demo/node/node" (in directory "/home/mark/Documents/github/gwt-material-demo"): error=2, No such file or directory -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following 

Hey kevzlou7979,

sorry for the late reply. The error seems familiar. What maven goal are you running? It works for me using mvn package. Also, the frontend-maven-plugin does not look for node path in your system, but inside /nodes_modules, so in case you tried to avoid the install-node-and-npm , this may cause it. I did not find enough flexibility in the frontend-maven-plugin to allow using the already installed npm and node. If you find a better way, please let me know. As for the code, I think this might be some misinterpretation from IntelliJ, the code works well if you try node serviceWorkerBuilder.js. Here is the full demo project: https://github.com/gwidgets/gwt-pwa-demo