chore: build single output dist file

.babelrc

@@ -1,5 +1,25 @@
 {
   "presets": [
-    "@babel/preset-env"
-  ]
+    [
+      "@babel/preset-env", {
+        "modules": "cjs"
+      }
+    ]
+  ],
+
+  "plugins": [
+    "add-module-exports"
+  ],
+
+  "env": {
+    "rollup": {
+      "presets": [
+        [
+          "@babel/preset-env", {
+            "modules": "false"
+          }
+        ]
+      ]
+    }
+  }
 }

package.json

@@ -45,22 +45,24 @@
     "@babel/preset-env": "7.9.0",
     "@babel/register": "7.9.0",
     "@types/prettier": "1.19.1",
+    "babel-plugin-add-module-exports": "1.0.2",
     "eslint": "6.8.0",
     "eslint-config-google": "0.14.0",
     "fancy-log": "1.3.3",
     "gulp": "4.0.2",
-    "gulp-babel": "8.0.0",
     "gulp-bump": "3.1.3",
     "gulp-conventional-changelog": "2.0.29",
     "gulp-eslint": "6.0.0",
     "gulp-git": "2.10.1",
     "gulp-jasmine": "4.0.0",
-    "gulp-prettier": "2.3.0",
     "jasmine-core": "3.5.0",
     "lodash.startswith": "4.2.1",
     "q": "1.5.1",
     "rimraf": "3.0.2",
     "rollup": "1.32.0",
+    "rollup-plugin-babel": "4.4.0",
+    "rollup-plugin-license": "1.0.0",
+    "rollup-plugin-strip-banner": "1.2.0",
     "tmp": "0.1.0"
   }
 }

scripts/build/index.js

@@ -22,15 +22,13 @@
  * SOFTWARE.
  */
 
-const path = require('path');
-const gulp = require('gulp');
-const babel = require('gulp-babel');
-const prettier = require('gulp-prettier');
-const config = require('../config');
+const rollup = require('rollup');
+const config = require('./rollup.config');
 
 module.exports = function build() {
-  return gulp.src(path.join(config.src, '*.js'))
-      .pipe(babel())
-      .pipe(prettier())
-      .pipe(gulp.dest(config.dist));
+  return rollup.rollup(config).then((bundle) => (
+    Promise.all(config.output.map((output) => (
+      bundle.write(output)
+    )))
+  ));
 };

scripts/build/rollup.config.js

@@ -0,0 +1,71 @@
+/**
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2017-2020 Mickael Jeanroy
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+const path = require('path');
+const prettier = require('prettier');
+const stripBanner = require('rollup-plugin-strip-banner');
+const babel = require('rollup-plugin-babel');
+const license = require('rollup-plugin-license');
+const config = require('../config');
+const pkg = require('../../package.json');
+
+module.exports = {
+  input: path.join(config.src, 'index.js'),
+
+  output: [
+    {
+      format: 'cjs',
+      file: path.join(config.dist, 'index.js'),
+    },
+  ],
+
+  plugins: [
+    stripBanner(),
+
+    babel({
+      envName: 'rollup',
+    }),
+
+    license({
+      banner: {
+        content: {
+          file: path.join(config.root, 'LICENSE'),
+        },
+      },
+    }),
+
+    {
+      renderChunk(code) {
+        return prettier.format(code, {
+          parser: 'babel',
+        });
+      },
+    },
+  ],
+
+  external: [
+    ...Object.keys(pkg.dependencies),
+    ...Object.keys(pkg.peerDependencies),
+  ],
+};