Fixes #21, add build step for mozilla-central with webpack, using existing code from Normandy.

README.md

@@ -341,6 +341,14 @@ it with Pip, and then run `therapist install` in this repo to set it
 up. It will automatically format your Javascript with Prettier, and
 run ESLint checks before committing your code.
 
+## Building a JSM for use in mozilla-central ##
+```shell
+$ yarn build
+```
+
+The result will be in `vendor/mozjexl.jsm`.  This is for use in `mozilla-central/toolkit`, so it is not
+minified as it will be compressed in the omnijar file.
+
 ## License
 Mozjexl is licensed under the MIT license. Please see `LICENSE.txt` for full
 details.

package.json

@@ -7,6 +7,8 @@
     "test": "test"
   },
   "scripts": {
+    "watch": "webpack --config ./webpack.config.js --watch",
+    "build": "webpack --config ./webpack.config.js",
     "test": "mocha -R spec --recursive test",
     "lint": "eslint lib test .eslintrc.js --ignore-pattern '!.eslintrc.js'"
   },
@@ -41,6 +43,8 @@
     "eslint": "^4.18.1",
     "eslint-config-prettier": "^2.9.0",
     "eslint-plugin-prettier": "^2.6.0",
-    "prettier": "^1.10.2"
+    "license-webpack-plugin": "0.5.1",
+    "prettier": "^1.10.2",
+    "webpack": "3.1.0"
   }
 }

webpack.config.js

@@ -0,0 +1,47 @@
+/* eslint-env node */
+const path = require("path");
+const webpack = require("webpack");
+const { ConcatSource } = require("webpack-sources");
+const LicenseWebpackPlugin = require("license-webpack-plugin");
+
+module.exports = {
+  context: __dirname,
+  entry: {
+    mozjexl: "./lib/Jexl.js"
+  },
+  output: {
+    path: path.resolve(__dirname, "vendor/"),
+    filename: "[name].jsm",
+    library: "[name].jsm",
+    libraryTarget: "this"
+  },
+  plugins: [
+    new webpack.DefinePlugin({
+      "process.env": {
+        NODE_ENV: JSON.stringify("production")
+      }
+    }),
+    /**
+     * Plugin that appends "this.EXPORTED_SYMBOLS = ["libname"]" to assets
+     * output by webpack. This allows built assets to be imported using
+     * Cu.import.
+     */
+    function ExportedSymbols() {
+      this.plugin("emit", function(compilation, callback) {
+        for (const libraryName in compilation.entrypoints) {
+          const assetName = `${libraryName}.jsm`; // Matches output.filename
+          compilation.assets[assetName] = new ConcatSource(
+            "/* eslint-disable */", // Disable linting
+            compilation.assets[assetName],
+            `this.EXPORTED_SYMBOLS = ["${libraryName}"];` // Matches output.library
+          );
+        }
+        callback();
+      });
+    },
+    new LicenseWebpackPlugin({
+      pattern: /^(MIT|ISC|MPL.*|Apache.*|BSD.*)$/,
+      filename: `LICENSE_THIRDPARTY`
+    })
+  ]
+};