refactor: add support for sw caching prefetched resources

packages/gatsby-plugin-offline/prefetch-catcher.js

@@ -0,0 +1,45 @@
+"use strict";
+
+var _interopRequireDefault = require("@babel/runtime/helpers/interopRequireDefault");
+
+var _regenerator = _interopRequireDefault(require("@babel/runtime/regenerator"));
+
+var _asyncToGenerator2 = _interopRequireDefault(require("@babel/runtime/helpers/asyncToGenerator"));
+
+self.addEventListener("message",
+/*#__PURE__*/
+function () {
+  var _ref2 = (0, _asyncToGenerator2.default)(
+  /*#__PURE__*/
+  _regenerator.default.mark(function _callee(_ref) {
+    var data, cache;
+    return _regenerator.default.wrap(function _callee$(_context) {
+      while (1) {
+        switch (_context.prev = _context.next) {
+          case 0:
+            data = _ref.data;
+
+            if (!(data.type === "prefetch")) {
+              _context.next = 6;
+              break;
+            }
+
+            _context.next = 4;
+            return caches.open("runtimecache");
+
+          case 4:
+            cache = _context.sent;
+            cache.addAll([data.pathname].concat(data.dependencies));
+
+          case 6:
+          case "end":
+            return _context.stop();
+        }
+      }
+    }, _callee, this);
+  }));
+
+  return function (_x) {
+    return _ref2.apply(this, arguments);
+  };
+}());

packages/gatsby-plugin-offline/src/gatsby-browser.js

@@ -1 +1,10 @@
 exports.registerServiceWorker = () => true
+
+exports.onPrefetchPathname = pathData => {
+  if (`serviceWorker` in navigator) {
+    navigator.serviceWorker.controller.postMessage({
+      type: `prefetch`,
+      ...pathData,
+    })
+  }
+}

packages/gatsby-plugin-offline/src/gatsby-node.js

@@ -69,6 +69,7 @@ exports.onPostBuild = (args, pluginOptions) => {
     })
 
   const options = {
+    importScripts: [`./prefetch-catcher.js`],
     staticFileGlobs: files.concat([
       `${rootDir}/index.html`,
       `${rootDir}/manifest.json`,

packages/gatsby-plugin-offline/src/prefetch-catcher.js

@@ -0,0 +1,6 @@
+self.addEventListener(`message`, async ({ data }) => {
+  if (data.type === `prefetch`) {
+    const cache = await caches.open(`runtimecache`)
+    cache.addAll([data.pathname, ...data.dependencies])
+  }
+})