fix: Changes to the UMD built file and npm package publishing

This patch introduces on top of #17 some minor changes from the
review comments, in particular:

- do not replace require("../filename") to include the api-metadata.json
  (restored the original '{/* include("...") */}' placeholder)
- raise an appropriate error message when the source file is used
  by mistake (or the "dist/" file has not been built correctly).
- set the generated UMD wrapped module as the package.json main
  entrypoint
- do not include api-metadata.json and src dir from the files included
  in the published npm package
- run both build and test npm scripts on prepublish

Gruntfile.js

@@ -28,7 +28,7 @@ module.exports = function(grunt) {
         options: {
           patterns: [
             {
-              match: /require\("..\/(.*?)"\)/,
+              match: /\{\/\* include\("(.*?)"\) \*\/\}/,
               replacement: (match, filename) => {
                 return grunt.file.read(filename)
                             .replace(/\n$/, "")

README.md

@@ -9,17 +9,18 @@ Chrome.
 
 ## Building
 
-To build, assuming you're already installed [npm](https://www.npmjs.com/),
-simply run:
+To build, assuming you're already installed [node >= 6](https://nodejs.org) and
+[npm](https://www.npmjs.com/), simply run:
 
 ```sh
 npm install
+npm run build
+npm run test
 ```
 
-This will build both non-minified and minified versions of the final library,
-and output them to `dist/browser-polyfill.js` and `dist/browser-polyfill.min.js`,
-respectively.
-
+This will install all the npm dependencies and build both non-minified and minified versions
+of the final library, and output them to `dist/browser-polyfill.js` and `dist/browser-polyfill.min.js`,
+respectively, and finally executes the unit tests on the generated dist files.
 
 ## Basic Setup
 
@@ -74,7 +75,6 @@ browser.tabs.executeScript({file: "content.js"}).then(result => {
 });
 ```
 
-
 ## Using the Promise-based APIs
 
 The Promise-based APIs in the `browser` namespace work, for the most part,

package.json

@@ -2,10 +2,8 @@
   "name": "webextension-polyfill",
   "version": "0.1.0",
   "description": "A lightweight polyfill library for Promise-based WebExtension APIs in Chrome.",
-  "main": "src/browser-polyfill.js",
+  "main": "dist/browser-polyfill.js",
   "files": [
-    "api-metadata.json",
-    "src",
     "dist"
   ],
   "repository": {
@@ -46,6 +44,6 @@
     "test": "mocha",
     "test-coverage": "COVERAGE=y nyc mocha",
     "publish-coverage": "grunt coveralls",
-    "prepublish": "npm run build"
+    "prepublish": "npm run build && npm run test"
   }
 }

src/browser-polyfill.js

@@ -13,9 +13,14 @@ if (typeof browser === "undefined") {
   // never actually need to be called, this allows the polyfill to be included
   // in Firefox nearly for free.
   const wrapAPIs = () => {
-    // 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
+    // NOTE: apiMetadata is associated to the content of the api-metadata.json file
+    // at build time by replacing the following "include" with the content of the
+    // JSON file.
+    const apiMetadata = {/* include("api-metadata.json") */};
+
+    if (Object.keys(apiMetadata).length === 0) {
+      throw new Error("api-metadata.json has not been included in browser-polyfill");
+    }
 
     /**
      * A WeakMap subclass which creates and stores a value for any key which does