Add mode to throw on invalid property access

README.md

@@ -332,7 +332,6 @@ be passed to eliminate the "power of" operator.
 $ yarn install
 $ yarn test
 ```
-
 ### Precommit hook
 
 Mozjexl provides a config for
@@ -341,6 +340,14 @@ 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.js`.  Though it is not named ".jsm", it will
+function as one.
+
 ## License
 Mozjexl is licensed under the MIT license. Please see `LICENSE.txt` for full
 details.

lib/Jexl.js

@@ -14,10 +14,11 @@ var Evaluator = require("./evaluator/Evaluator"),
  * xpath-like drilldown into native Javascript objects.
  * @constructor
  */
-function Jexl() {
+function Jexl(throwOnMissingProp = false) {
   this._customGrammar = null;
   this._lexer = null;
   this._transforms = {};
+  this._throwOnMissingProp = throwOnMissingProp;
 }
 
 /**

lib/evaluator/handlers.js

@@ -83,6 +83,14 @@ exports.FilterExpression = function(ast) {
 exports.Identifier = function(ast) {
   if (ast.from) {
     return this.eval(ast.from).then(function(context) {
+      if (
+        this._throwOnMissingProp &&
+        !Object.hasOwnProperty(context, ast.value)
+      ) {
+        throw new Error(
+          `property does not have an identifier named ${ast.value}`
+        );
+      }
       if (Array.isArray(context)) context = context[0];
       if (context === undefined) return undefined;
       return context[ast.value];

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'"
   },
@@ -35,12 +37,15 @@
   },
   "homepage": "https://github.com/mozilla/mozjexl",
   "devDependencies": {
+    "babili-webpack-plugin": "0.1.2",
     "chai": "^2.0.0",
     "chai-as-promised": "^4.2.0",
     "mocha": "^2.1.0",
     "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"
   }
 }