feat: library wrapped as an UMD module

This addresses [issue 7] by making it possible for users to run:

```sh
npm install webextension-polyfill
```

and download a module that they can use with a bundler as follows:

```js
import browser from 'webextension-polyfill';
```

Also, add a [prepublish script] so that users who clone the repo don't
need to run `grunt` manually. In addition, specify [files] in
package.json so that this module can be published to npm without
including miscellanea. This can be verified by running:

```sh
npm pack && tar -tvf webextension-polyfill-0.1.0.tgz
```

[issue 7]: https://github.com/mozilla/webextension-polyfill/issues/7
[files]: https://docs.npmjs.com/files/package.json#files
[prepublish script]: https://docs.npmjs.com/misc/scripts

Gruntfile.js

@@ -28,7 +28,7 @@ module.exports = function(grunt) {
         options: {
           patterns: [
             {
-              match: /\{\/\* include\("(.*?)"\) \*\/\}/,
+              match: /require\("..\/(.*?)"\)/,
               replacement: (match, filename) => {
                 return grunt.file.read(filename)
                             .replace(/\n$/, "")
@@ -55,6 +55,15 @@ module.exports = function(grunt) {
       },
     },
 
+    umd: {
+      all: {
+        src: "dist/browser-polyfill.js",
+        template: "unit",
+        globalAlias: "browser",
+        amdModuleId: "webextension-polyfill",
+      },
+    },
+
     "closure-compiler": {
       dist: {
         files: {
@@ -88,8 +97,9 @@ module.exports = function(grunt) {
 
   grunt.loadNpmTasks("gruntify-eslint");
   grunt.loadNpmTasks("grunt-replace");
+  grunt.loadNpmTasks("grunt-umd");
   grunt.loadNpmTasks("grunt-coveralls");
   require("google-closure-compiler").grunt(grunt);
 
-  grunt.registerTask("default", ["eslint", "replace", "closure-compiler"]);
+  grunt.registerTask("default", ["eslint", "replace", "umd", "closure-compiler"]);
 };

README.md

@@ -14,7 +14,6 @@ simply run:
 
 ```sh
 npm install
-grunt
 ```
 
 This will build both non-minified and minified versions of the final library,

package.json

@@ -2,6 +2,12 @@
   "name": "webextension-polyfill",
   "version": "0.1.0",
   "description": "A lightweight polyfill library for Promise-based WebExtension APIs in Chrome.",
+  "main": "src/browser-polyfill.js",
+  "files": [
+    "api-metadata.json",
+    "src",
+    "dist"
+  ],
   "repository": {
     "type": "git",
     "url": "git+https://github.com/mozilla/webextension-polyfill.git"
@@ -19,6 +25,7 @@
     "grunt": "^1.0.1",
     "grunt-coveralls": "^1.0.1",
     "grunt-replace": "*",
+    "grunt-umd": "^2.4.0",
     "gruntify-eslint": "*",
     "istanbul-lib-instrument": "^1.1.3",
     "jsdom": "^9.6.0",
@@ -38,6 +45,7 @@
     "build": "grunt",
     "test": "mocha",
     "test-coverage": "COVERAGE=y nyc mocha",
-    "publish-coverage": "grunt coveralls"
+    "publish-coverage": "grunt coveralls",
+    "prepublish": "npm run build"
   }
 }

src/browser-polyfill.js

@@ -13,7 +13,9 @@ if (typeof browser === "undefined") {
   // never actually need to be called, this allows the polyfill to be included
   // in Firefox nearly for free.
   const wrapAPIs = () => {
-    const apiMetadata = {/* include("api-metadata.json") */};
+    // Note that `require` does NOT work in general. See discussion here:
+    // https://github.com/mozilla/webextension-polyfill/pull/17#discussion_r99170958
+    const apiMetadata = require("../api-metadata.json"); // eslint-disable-line no-undef
 
     /**
      * A WeakMap subclass which creates and stores a value for any key which does
@@ -336,5 +338,9 @@ if (typeof browser === "undefined") {
     return wrapObject(chrome, staticWrappers, apiMetadata);
   };
 
-  this.browser = wrapAPIs();
+  // The build process adds a UMD wrapper around this file, which makes the
+  // `module` variable available.
+  module.exports = wrapAPIs(); // eslint-disable-line no-undef
+} else {
+  module.exports = browser; // eslint-disable-line no-undef
 }

test/helpers.js

@@ -0,0 +1,32 @@
+"use strict";
+
+const {deepEqual, equal, ok} = require("chai").assert;
+
+module.exports.testCustomProperties = window => {
+  Object.defineProperty(window.browser, "myns", {
+    enumerable: true,
+    configurable: true,
+    value: {mykey: true},
+  });
+
+  ok("myns" in window.browser, "The custom property exists");
+  ok("mykey" in window.browser.myns,
+     "The content of the custom property exists");
+
+  deepEqual(window.browser.myns, {mykey: true},
+            "The custom property has the expected content");
+
+  delete window.browser.myns;
+
+  ok(!("myns" in window.browser),
+     "The deleted custom defined property has been removed");
+};
+
+module.exports.testUndefinedProperties = window => {
+  equal(window.browser.myns.mykey, true,
+        "Got the expected result from a wrapped property");
+  equal(window.browser.myns.nonexistent, undefined,
+        "Got undefined for non existent property");
+  equal(window.browser.nonexistent, undefined,
+        "Got undefined for non existent namespaces");
+};

test/test-browser-global.js

@@ -1,9 +1,11 @@
 "use strict";
 
-const {deepEqual, equal, ok} = require("chai").assert;
+const {deepEqual, equal} = require("chai").assert;
 
 const {setupTestDOMWindow} = require("./setup");
 
+const {testCustomProperties, testUndefinedProperties} = require("./helpers");
+
 describe("browser-polyfill", () => {
   it("wraps the global chrome namespace with a global browser namespace", () => {
     const fakeChrome = {};
@@ -29,37 +31,12 @@ describe("browser-polyfill", () => {
   describe("browser wrapper", () => {
     it("supports custom properties defined using Object.defineProperty", () => {
       const fakeChrome = {};
-      return setupTestDOMWindow(fakeChrome).then(window => {
+      return setupTestDOMWindow(fakeChrome).then(testCustomProperties);
-        Object.defineProperty(window.browser, "myns", {
-          enumerable: true,
-          configurable: true,
-          value: {mykey: true},
-        });
-
-        ok("myns" in window.browser, "The custom property exists");
-        ok("mykey" in window.browser.myns,
-           "The content of the custom property exists");
-
-        deepEqual(window.browser.myns, {mykey: true},
-                  "The custom property has the expected content");
-
-        delete window.browser.myns;
-
-        ok(!("myns" in window.browser),
-           "The deleted custom defined property has been removed");
-      });
     });
 
     it("returns undefined for property undefined in the target", () => {
       const fakeChrome = {myns: {mykey: true}};
-      return setupTestDOMWindow(fakeChrome).then(window => {
+      return setupTestDOMWindow(fakeChrome).then(testUndefinedProperties);
-        equal(window.browser.myns.mykey, true,
-              "Got the expected result from a wrapped property");
-        equal(window.browser.myns.nonexistent, undefined,
-              "Got undefined for non existent property");
-        equal(window.browser.nonexistent, undefined,
-              "Got undefined for non existent namespaces");
-      });
     });
   });
 });

test/test-node-export.js

@@ -0,0 +1,47 @@
+"use strict";
+
+const {deepEqual, strictEqual, notStrictEqual, throws} = require("chai").assert;
+const {testCustomProperties, testUndefinedProperties} = require("./helpers");
+
+describe("node-export", () => {
+  beforeEach(() => {
+    delete global.browser;
+    delete global.chrome;
+    delete require.cache[require.resolve("../")];
+  });
+
+  it("exports the global browser namespace if it already exists", () => {
+    global.browser = {key: "value"};
+
+    const exported = require("../");
+
+    strictEqual(exported, browser);
+  });
+
+  it("exports a wrapper around the global chrome namespace", () => {
+    global.chrome = {key: "value"};
+
+    const exported = require("../");
+
+    deepEqual(exported, chrome);
+    notStrictEqual(exported, chrome);
+  });
+
+  it("throws an error if the global chrome namespace is missing", () => {
+    throws(() => require("../"), ReferenceError, /chrome is not defined/);
+  });
+
+  describe("browser wrapper", () => {
+    it("supports custom properties defined using Object.defineProperty", () => {
+      global.chrome = {};
+      global.browser = require("../");
+      testCustomProperties(global);
+    });
+
+    it("returns undefined for property undefined in the target", () => {
+      global.chrome = {myns: {mykey: true}};
+      global.browser = require("../");
+      testUndefinedProperties(global);
+    });
+  });
+});