fix: Throw error when loaded in non-extension contexts (#190)

Fixes #186

src/browser-polyfill.js

@@ -508,6 +508,10 @@ if (typeof browser === "undefined" || Object.getPrototypeOf(browser) !== Object.
     return wrapObject(extensionAPIs, staticWrappers, apiMetadata);
   };
 
+  if (typeof chrome != "object" || !chrome || !chrome.runtime || !chrome.runtime.id) {
+    throw new Error("This script should only be loaded in a browser extension.");
+  }
+
   // The build process adds a UMD wrapper around this file, which makes the
   // `module` variable available.
   module.exports = wrapAPIs(chrome);

test/setup.js

@@ -37,6 +37,17 @@ function setupTestDOMWindow(chromeObject, browserObject = undefined) {
   return new Promise((resolve, reject) => {
     const window = testDOMWindow;
 
+    // Ensure that "chrome.runtime.id" is set, because the polyfill is only
+    // loaded in extension environments.
+    if (chromeObject) {
+      if (!chromeObject.runtime) {
+        chromeObject.runtime = {};
+      }
+      if (!chromeObject.runtime.id) {
+        chromeObject.runtime.id = "some-test-id-from-test-setup";
+      }
+    }
+
     // Inject the fake chrome object used as a fixture for the particular
     // browser-polyfill test scenario.
     window.chrome = chromeObject;

test/test-browser-global.js

@@ -5,6 +5,17 @@ const {deepEqual, equal, ok} = require("chai").assert;
 const {setupTestDOMWindow} = require("./setup");
 
 describe("browser-polyfill", () => {
+  it("throws an error in a non-extension environment", async () => {
+    try {
+      await setupTestDOMWindow(null);
+      ok(false, "The polyfill script should have failed to load.");
+    } catch (e) {
+      equal(e.message,
+            "This script should only be loaded in a browser extension.",
+            "Expected script to not load in a non-extension environment");
+    }
+  });
+
   it("wraps the global chrome namespace with a global browser namespace", () => {
     const fakeChrome = {};
     return setupTestDOMWindow(fakeChrome).then(window => {

test/test-proxied-properties.js

@@ -159,9 +159,16 @@ describe("browser-polyfill", () => {
           Object.defineProperty(this, "runtime", {value});
           return value;
         },
+        get tabs() {
+          ok(false, "chrome.tabs should not lazily be initialized without explicit API call");
+        },
       };
       return setupTestDOMWindow(fakeChrome).then(window => {
-        equal(lazyInitCount, 0, "chrome.runtime should not be initialized without explicit API call");
+        // This used to be equal(lazyInitCount, 0, ...), but was changed to
+        // accomodate a change in the implementation of the polyfill.
+        // To verify that APIs are not unnecessarily initialized, the fakeChrome
+        // object has a "tabs" getter that fails the test upon access.
+        equal(lazyInitCount, 1, "chrome.runtime should be initialized because chrome.runtime.id is accessed during polyfill initialization");
 
         window.browser.runtime.onMessage.addListener(() => {});
         equal(lazyInitCount, 1, "chrome.runtime should be initialized upon accessing browser.runtime");