From f2e59095fa08eae5b7141a80aadede85966c8f13 Mon Sep 17 00:00:00 2001
From: Bogdan Chadkin <trysound@yandex.ru>
Date: Wed, 30 Jan 2019 18:26:44 +0300
Subject: [PATCH] chore(build): provide esm support for bundlers (#1197)

In this diff I added esm bundle which will allow user bundlers
to produce much smaller code. Currently regular babel output is
wrapped with module iife.

This project has a lot of files so with single esm file users will
bundle it slightly faster.

As a bonus we see the size of the project without dependencies.
---
 .size-snapshot.json | 26 ++++++++++++++++++++------
 package.json        |  1 +
 rollup.config.js    |  9 +++++++++
 3 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/.size-snapshot.json b/.size-snapshot.json
index d5fd570f0..0d9086514 100644
--- a/.size-snapshot.json
+++ b/.size-snapshot.json
@@ -1,12 +1,26 @@
 {
   "./dist/react-big-calendar.js": {
-    "bundled": 469894,
-    "minified": 152522,
-    "gzipped": 42174
+    "bundled": 470853,
+    "minified": 153064,
+    "gzipped": 42298
   },
   "./dist/react-big-calendar.min.js": {
-    "bundled": 412865,
-    "minified": 135555,
-    "gzipped": 38300
+    "bundled": 413805,
+    "minified": 136004,
+    "gzipped": 38362
+  },
+  "dist/react-big-calendar.esm.js": {
+    "bundled": 167523,
+    "minified": 80477,
+    "gzipped": 19800,
+    "treeshaked": {
+      "rollup": {
+        "code": 62050,
+        "import_statements": 1470
+      },
+      "webpack": {
+        "code": 65556
+      }
+    }
   }
 }
diff --git a/package.json b/package.json
index 2623eb5db..44fe12bb4 100644
--- a/package.json
+++ b/package.json
@@ -6,6 +6,7 @@
   "repository": "intljusticemission/react-big-calendar",
   "license": "MIT",
   "main": "lib/index.js",
+  "module": "dist/react-big-calendar.esm.js",
   "style": "lib/css/react-big-calendar.css",
   "files": [
     "lib/",
diff --git a/rollup.config.js b/rollup.config.js
index 07f5605cf..9fb8795b8 100644
--- a/rollup.config.js
+++ b/rollup.config.js
@@ -4,6 +4,7 @@ import commonjs from 'rollup-plugin-commonjs'
 import replace from 'rollup-plugin-replace'
 import { sizeSnapshot } from 'rollup-plugin-size-snapshot'
 import { terser } from 'rollup-plugin-terser'
+import pkg from './package.json'
 
 const input = './src/index.js'
 const name = 'ReactBigCalendar'
@@ -58,4 +59,12 @@ export default [
       terser(),
     ],
   },
+
+  {
+    input,
+    output: { file: pkg.module, format: 'esm' },
+    // prevent bundling all dependencies
+    external: id => !id.startsWith('.') && !id.startsWith('/'),
+    plugins: [babel(babelOptions), sizeSnapshot()],
+  },
 ]