Support spec option (#98)

experimental/babel-preset-env/README.md

@@ -132,6 +132,12 @@ To prevent these errors - specify the uglify option, which will enable all plugi
 
 > NOTE: Uglify has a work-in-progress "Harmony" branch to address the lack of ES6 support, but it is not yet stable.  You can follow its progress in [UglifyJS2 issue #448](https://github.com/mishoo/UglifyJS2/issues/448).  If you require an alternative minifier which _does_ support ES6 syntax, we recommend using [Babili](https://github.com/babel/babili).
 
+### `spec`
+
+`boolean`, defaults to `false`.
+
+Enable more spec compliant, but potentially slower, transformations for any plugins in this preset that support them.
+
 ### `loose`
 
 `boolean`, defaults to `false`.

experimental/babel-preset-env/src/index.js

@@ -165,13 +165,12 @@ function getPlatformSpecificDefaultFor(targets) {
 
 export default function buildPreset(context, opts = {}) {
   const validatedOptions = normalizeOptions(opts);
-  const { debug, loose, moduleType, useBuiltIns } = validatedOptions;
+  const { debug, loose, moduleType, spec, useBuiltIns } = validatedOptions;
 
   const targets = getTargets(validatedOptions.targets);
   const include = transformIncludesAndExcludes(validatedOptions.include);
   const exclude = transformIncludesAndExcludes(validatedOptions.exclude);
 
-
   const filterPlugins = filterItem.bind(null, targets, exclude.plugins, pluginList);
   const transformations = Object.keys(pluginList)
     .filter(filterPlugins)
@@ -210,11 +209,13 @@ export default function buildPreset(context, opts = {}) {
   const modulePlugin = moduleType !== false && moduleTransformations[moduleType];
   const plugins = [];
 
+  // NOTE: not giving spec here yet to avoid compatibility issues when
+  // babel-plugin-transform-es2015-modules-commonjs gets its spec mode
   modulePlugin &&
     plugins.push([require(`babel-plugin-${modulePlugin}`), { loose }]);
 
   plugins.push(...transformations.map((pluginName) =>
-    [require(`babel-plugin-${pluginName}`), { loose }]
+    [require(`babel-plugin-${pluginName}`), { spec, loose }]
   ));
 
   useBuiltIns &&

experimental/babel-preset-env/src/normalize-options.js

@@ -53,15 +53,21 @@ export const checkDuplicateIncludeExcludes = (include = [], exclude = []) => {
   );
 };
 
-export const validateLooseOption = (looseOpt = false) => {
-  invariant(
-    typeof looseOpt === "boolean",
-    "Invalid Option: The 'loose' option must be a boolean."
-  );
+export const validateBoolOption = (name, value, defaultValue) => {
+  if (typeof value === "undefined") {
+    value = defaultValue;
+  }
 
-  return looseOpt;
+  if (typeof value !== "boolean") {
+    throw new Error(`Preset env: '${name}' option must be a boolean.`);
+  }
+
+  return value;
 };
 
+export const validateLooseOption = (looseOpt) => validateBoolOption("loose", looseOpt, false);
+export const validateSpecOption = (specOpt) => validateBoolOption("spec", specOpt, false);
+
 export const validateModulesOption = (modulesOpt = "commonjs") => {
   invariant(
     modulesOpt === false || Object.keys(moduleTransformations).indexOf(modulesOpt) > -1,
@@ -104,6 +110,7 @@ export default function normalizeOptions(opts) {
     include: validateIncludesAndExcludes(opts.include, "include"),
     loose: validateLooseOption(opts.loose),
     moduleType: validateModulesOption(opts.modules),
+    spec: validateSpecOption(opts.spec),
     targets: opts.targets,
     useBuiltIns: opts.useBuiltIns
   };

experimental/babel-preset-env/test/fixtures/preset-options/spec/actual.js

@@ -0,0 +1,2 @@
+const bar = "bar";
+const x = () => `foo${bar}`;

experimental/babel-preset-env/test/fixtures/preset-options/spec/expected.js

@@ -0,0 +1,10 @@
+"use strict";
+
+function _newArrowCheck(innerThis, boundThis) { if (innerThis !== boundThis) { throw new TypeError("Cannot instantiate an arrow function"); } }
+
+var bar = "bar";
+var x = function () {
+  _newArrowCheck(undefined, undefined);
+
+  return "foo" + bar;
+}.bind(undefined);

experimental/babel-preset-env/test/fixtures/preset-options/spec/options.json

@@ -0,0 +1,7 @@
+{
+  "presets": [
+    ["../../../../lib", {
+      "spec": true
+    }]
+  ]
+}

experimental/babel-preset-env/test/normalize-options.spec.js

@@ -5,10 +5,11 @@ const assert = require("assert");
 
 const {
   checkDuplicateIncludeExcludes,
+  normalizePluginNames,
   validateIncludesAndExcludes,
   validateLooseOption,
   validateModulesOption,
-  normalizePluginNames
+  validateSpecOption,
 } = normalizeOptions;
 
 describe("normalize-options", () => {
@@ -60,6 +61,20 @@ describe("normalize-options", () => {
     });
   });
 
+  describe("validateSpecOption", () => {
+    it("`undefined` option returns false", () => {
+      assert(validateSpecOption() === false);
+    });
+
+    it("`false` option returns false", () => {
+      assert(validateSpecOption(false) === false);
+    });
+
+    it("`true` option returns true", () => {
+      assert(validateSpecOption(true) === true);
+    });
+  });
+
   describe("checkDuplicateIncludeExcludes", function() {
     it("should throw if duplicate names in both", function() {
       assert.throws(() => {