Add sw-precache to WSK.

app/scripts/main.js

@@ -19,6 +19,55 @@
 (function() {
   'use strict';
 
+  // Check to make sure service workers are supported in the current browser,
+  // and that the current page is accessed from a secure origin. Using a
+  // service worker from an insecure origin will trigger JS console errors. See
+  // http://www.chromium.org/Home/chromium-security/prefer-secure-origins-for-powerful-new-features
+  if ('serviceWorker' in navigator &&
+      (window.location.protocol === 'https:' ||
+       window.location.hostname === 'localhost' ||
+       window.location.hostname.indexOf('127.') === 0)) {
+    navigator.serviceWorker.register('/service-worker.js', {
+      scope: './'
+    }).then(function(registration) {
+      // Check to see if there's an updated version of service-worker.js with
+      // new files to cache:
+      // https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#service-worker-registration-update-method
+      if (typeof registration.update === 'function') {
+        registration.update();
+      }
+
+      // updatefound is fired if service-worker.js changes.
+      registration.onupdatefound = function() {
+        // updatefound is also fired the very first time the SW is installed,
+        // and there's no need to prompt for a reload at that point.
+        // So check here to see if the page is already controlled,
+        // i.e. whether there's an existing service worker.
+        if (navigator.serviceWorker.controller) {
+          // The updatefound event implies that registration.installing is set:
+          // https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#service-worker-container-updatefound-event
+          var installingWorker = registration.installing;
+
+          installingWorker.onstatechange = function() {
+            switch (installingWorker.state) {
+              case 'installed':
+                // At this point, the old content will have been purged and the
+                // fresh content will have been added to the cache.
+                // It's the perfect time to display a "New content is
+                // available; please refresh." message in the page's interface.
+                break;
+
+              case 'redundant':
+                throw 'The installing service worker became redundant.';
+            }
+          };
+        }
+      };
+    }).catch(function(e) {
+      console.error('Error during service worker registration:', e);
+    });
+  }
+
   // Your custom JavaScript goes here
 
 })();

app/service-worker.js

@@ -0,0 +1,4 @@
+// This file is intentionally without code.
+// It's present so that service worker registration will work when serving from the 'app' directory.
+// The version of service-worker.js that's present in the 'dist' directory is automatically
+// generated by the 'generate-service-worker' gulp task, and contains code to precache resources.

gulpfile.js

@@ -27,6 +27,10 @@ var runSequence = require('run-sequence');
 var browserSync = require('browser-sync');
 var pagespeed = require('psi');
 var reload = browserSync.reload;
+var swPrecache = require('sw-precache');
+var fs = require('fs');
+var path = require('path');
+var packageJson = require('./package.json');
 
 // Lint JavaScript
 gulp.task('jshint', function() {
@@ -187,7 +191,11 @@ gulp.task('serve:dist', ['default'], function() {
 
 // Build Production Files, the Default Task
 gulp.task('default', ['clean'], function(cb) {
-  runSequence('styles', ['jshint', 'html', 'scripts', 'images', 'styleguide-images', 'fonts', 'copy'], cb);
+  runSequence(
+    'styles',
+    ['jshint', 'html', 'scripts', 'images', 'styleguide-images', 'fonts', 'copy'],
+    'generate-service-worker',
+    cb);
 });
 
 // Run PageSpeed Insights
@@ -201,5 +209,50 @@ gulp.task('pagespeed', function (cb) {
   }, cb);
 });
 
+// See http://www.html5rocks.com/en/tutorials/service-worker/introduction/ for
+// an in-depth explanation of what service workers are and why you should care.
+// Generate a service worker file that will provide offline functionality for
+// local resources. This should only be done for the 'dist' directory, to allow
+// live reload to work as expected when serving from the 'app' directory.
+gulp.task('generate-service-worker', function(callback) {
+  var rootDir = 'dist';
+
+  swPrecache({
+    // Used to avoid cache conflicts when serving on localhost.
+    cacheId: packageJson.name || 'web-starter-kit',
+    // URLs that don't directly map to single static files can be defined here.
+    // If any of the files a URL depends on changes, then the URL's cache entry
+    // is invalidated and it will be refetched.
+    // Generally, URLs that depend on multiple files (such as layout templates)
+    // should list all the files; a change in any will invalidate the cache.
+    // In this case, './' is the top-level relative URL, and its response
+    // depends on the contents of the file 'dist/index.html'.
+    dynamicUrlToDependencies: {
+      './': [path.join(rootDir, 'index.html')]
+    },
+    staticFileGlobs: [
+      // Add/remove glob patterns to match your directory setup.
+      rootDir + '/fonts/**/*.woff',
+      rootDir + '/images/**/*',
+      rootDir + '/scripts/**/*.js',
+      rootDir + '/styles/**/*.css',
+      rootDir + '/*.{html,json}'
+    ],
+    // Translates a static file path to the relative URL that it's served from.
+    stripPrefix: path.join(rootDir, path.sep)
+  }, function(error, serviceWorkerFileContents) {
+    if (error) {
+      return callback(error);
+    }
+    fs.writeFile(path.join(rootDir, 'service-worker.js'),
+      serviceWorkerFileContents, function(error) {
+      if (error) {
+        return callback(error);
+      }
+      callback();
+    });
+  });
+});
+
 // Load custom tasks from the `tasks` directory
 // try { require('require-dir')('tasks'); } catch (err) { console.error(err); }

package.json

@@ -25,7 +25,8 @@
     "opn": "^1.0.0",
     "psi": "^1.0.4",
     "require-dir": "^0.1.0",
-    "run-sequence": "^1.0.2"
+    "run-sequence": "^1.0.2",
+    "sw-precache": "^1.2.1"
   },
   "engines": {
     "node": ">=0.10.0"