build bootstrap in esm

build/rollup.config.js

@@ -6,8 +6,10 @@ const resolve = require('rollup-plugin-node-resolve')
 const banner = require('./banner.js')
 
 const BUNDLE = process.env.BUNDLE === 'true'
+const ESM = process.env.ESM === 'true'
 
-let fileDest = 'bootstrap.js'
+let fileDest = `bootstrap${ESM ? '.esm' : ''}.js`
+const indexPath = ESM ? '../js/index.esm.js' : '../js/index.umd.js'
 const external = ['popper.js']
 const plugins = [
   babel({
@@ -28,22 +30,27 @@ const globals = {
 }
 
 if (BUNDLE) {
-  fileDest = 'bootstrap.bundle.js'
+  fileDest = `bootstrap${ESM ? '.esm' : ''}.bundle.js`
   // Remove last entry in external array to bundle Popper
   external.pop()
   delete globals['popper.js']
   plugins.push(resolve())
 }
 
-module.exports = {
-  input: path.resolve(__dirname, '../js/src/index.js'),
+const rollupConfig = {
+  input: path.resolve(__dirname, indexPath),
   output: {
     banner,
     file: path.resolve(__dirname, `../dist/js/${fileDest}`),
-    format: 'umd',
-    globals,
-    name: 'bootstrap'
+    format: ESM ? 'esm' : 'umd',
+    globals
   },
   external,
   plugins
 }
+
+if (!ESM) {
+  rollupConfig.output.name = 'bootstrap'
+}
+
+module.exports = rollupConfig