feat(pgk): use es for modern js, change module field for es5 + esmodule

Fixes #78

Author: stevemao

README.md

@@ -26,25 +26,17 @@ npm install autobind-decorator
 
 We target IE11+ browsers (see [out browserslist](./src/browserslist)) with the following caveats:
 
-`main` entry is in ES5
+`main`: ES5
 
-`module` entry is in ES6+ (notably ES modules to enable tree shaking)
+`module`: ES5 + ES modules to enable tree shaking
 
-#### Dev
-
-node 8.10+ with latest npm
+`es`: modern JS
 
-## ES5 and uglify users
+On consuming modern JS, you can transpile the script to your target environment ([@babel/preset-env](https://babeljs.io/docs/en/babel-preset-env) is recommended) to minimise the cost. For more details, please read https://babeljs.io/blog/2018/06/26/on-consuming-and-publishing-es2015+-packages.
 
-Starting from v2.2, we added `module` entry in package.json and kept `main` entry as is. `module` entry is for those who wish to use modern JavaScript (notably ES modules to enable tree shaking). If your environment doesn't understand the modern syntax, you can configure your tool to read the ES5 script via the `main` entry. EG: with webpack, you could do
-
-```js
-resolve: {
-  mainFields: ['main']
-}
-```
+#### Dev
 
-You could also transpile the script to your target environment ([@babel/preset-env](https://babeljs.io/docs/en/babel-preset-env) is recommended). For more details, please read https://babeljs.io/blog/2018/06/26/on-consuming-and-publishing-es2015+-packages.
+node 8.10+ with latest npm
 
 ## Babel 6 users (legacy only)
 

package.json

@@ -2,12 +2,16 @@
   "name": "autobind-decorator",
   "version": "2.3.1",
   "description": "Decorator for binding method to an object",
-  "main": "lib/index.js",
-  "module": "src/index.js",
+  "main": "lib/cjs/index.js",
+  "module": "lib/esm/index.js",
+  "es": "src/index.js",
   "types": "index.d.ts",
   "scripts": {
     "clean": "rm -rf lib",
-    "prepare": " npm run clean && babel src --out-dir lib --ignore \"src/__tests__/*.js\"",
+    "build:es5": "babel src --out-dir lib/cjs --ignore \"src/__tests__/*.js\"",
+    "build:module": "babel --no-babelrc --config-file ./src/.babelrc.es.js src --out-dir lib/esm --ignore \"src/__tests__/*.js\"",
+    "build": "npm run build:es5 && npm run build:module",
+    "prepare": " npm run clean && npm run build",
     "lint": "xo",
     "test": "jest --coverage",
     "release": "standard-version",

src/.babelrc

@@ -0,0 +1,9 @@
+module.exports = {
+  "presets": [
+    ["@babel/preset-env",
+      {
+        "modules": false,
+      }
+    ]
+  ]
+}

src/.babelrc.es.js

@@ -0,0 +1,5 @@
+module.exports = {
+  "presets": [
+    ["@babel/preset-env"]
+  ]
+}