ES modules exports (implements #2718)

.eslintrc

@@ -3,5 +3,8 @@
     "browser": true,
     "node": true,
     "amd": true
+  },
+  "parserOptions": {
+    "ecmaVersion": 3
   }
 }

.gitignore

@@ -5,3 +5,5 @@ node_modules
 *.swp
 nyc_output
 coverage
+test-treeshake/*-umd.js
+docs/underscore.js

CONTRIBUTING.md

@@ -8,6 +8,6 @@
 
 * Before sending a pull request for a feature, be sure to have [tests](https://underscorejs.org/test/).
 
-* Use the same coding style as the rest of the [codebase](https://github.com/jashkenas/underscore/blob/master/underscore.js).
+* Use the same coding style as the rest of the [codebase](https://github.com/jashkenas/underscore/blob/master/modules/index.js).
 
 * In your pull request, do not add documentation or re-build the minified `underscore-min.js` file. We'll do those things before cutting a new release.

docs/.eslintrc

@@ -1,5 +1,7 @@
 {
   "globals": {
-      "_": true
+      "_": true,
+      "parserOptions": {},
+      "rules": [],
   }
 }

docs/rollup.config.js

@@ -0,0 +1,14 @@
+module.exports = {
+  input: '../modules/index-all.js',
+  treeshake: false,
+  context: 'this',
+  output: {
+    file: 'underscore.js',
+    exports: 'named',
+    format: 'esm',
+    legacy: true,
+    strict: false,
+    externalLiveBindings: false,
+    freeze: false,
+  },
+};

modules/.eslintrc

@@ -0,0 +1,12 @@
+{
+  "parserOptions": {
+    "ecmaVersion": 6,
+    "sourceType": "module",
+  },
+  "plugins": [
+    "import"
+  ],
+  "extends": [
+    "plugin:import/errors"
+  ]
+}

modules/index-all.js

@@ -0,0 +1,2 @@
+export { default } from './index-default';
+export * from './index';

modules/index-default.js

@@ -0,0 +1,5 @@
+import * as allExports from './index';
+import { mixin } from './index';
+
+// Add all of the Underscore functions to the wrapper object and return it.
+export default mixin(allExports);